Wednesday, November 28, 2007

C Interview Questions

1. Write a program in C to find the 3*3 matrix multiplication.

2. Write a program in C to find the complex number of a given number.

3. how to print all the combinations of a given integer.

4. what is the significance of following functions

  • freopen()
  • strtok()
  • access()
  • state()
5. what is the "escape hatch" provided by #pragma directive?

6. what is source code of this tringle ...

7. What happens when you overload the stack?

8. what do you mean by preprocessor directory?

9. What is byte offset of a field within a structure?

10. What is unabridged list?

11. How is structure passing and returning implemented?

12. Write sample code or algorithim to get all possible combinations of data that will be entered from keyboard.

13. Explian Floyd Cycle finding algorithm for circular link list?

14. Why is that a pointer is depicted by '*' in C?

15. Write a program to print an 2D array in spiral manner

16. #includevoid fun(int);void main(){ inta; a=3; fun(a); }void fun(int){ if(n>0) { fun(--n);...

17. Given the values of two nodes in a *binary search tree*, write a cprogram to find the lowest common ancestor.

18. Can we define an array without any constant expression? If Yes, How?

19. For what purpose pragma.h header file is used?

20. What is the advantage of zero filling in calloc() ?

Oracle Interview Questions - Part 13

1.What are the various types of Exceptions ?
User defined and Predefined Exceptions.

2.Can we define exceptions twice in same block ?

3.What is the difference between a procedure and a function ?
Functions return a single variable by value whereas procedures do not return any variable by value. Rather they return multiple variables by passing variables by reference through their OUT parameter.

4.Can you have two functions with the same name in a PL/SQL block ?

5.Can you have two stored functions with the same name ?

6.Can you call a stored function in the constraint of a table ?

7.What are the various types of parameter modes in a procedure ?

8.What is Over Loading and what are its restrictions ?
OverLoading means an object performing different functions depending upon the no. of parameters or the data type of the parameters passed to it.

9.Can functions be overloaded ?

10.Can 2 functions have same name & input parameters but differ only by return datatype?
11.What are the constructs of a procedure, function or a package ?
The constructs of a procedure, function or a package are : variables and constants cursors exceptions

12.Why Create or Replace and not Drop and recreate procedures ?
So that Grants are not dropped.

13.Can you pass parameters in packages ? How ?
Yes. You can pass parameters to procedures or functions in a package.

14.What are the parts of a database trigger ?
The parts of a trigger are:
A triggering event or statement
A trigger restriction
A trigger action

15.What are the various types of database triggers ?
There are 12 types of triggers, they are combination of :
Insert, Delete and Update Triggers.
Before and After Triggers.
Row and Statement Triggers.(3*2*2=12)

16.What is the advantage of a stored procedure over a database trigger ?
We have control over the firing of a stored procedure but we have no control over the firing of a trigger.

17.What is the maximum no. of statements that can be specified in a trigger statement ?

18.Can views be specified in a trigger statement ?

19.What are the values of :new and :old in Insert/Delete/Update Triggers ?
INSERT : new = new value, old = NULL
DELETE : new = NULL, old = old value
UPDATE : new = new value, old = old value

20.What are cascading triggers? What is the maximum no of cascading triggers at a time?
When a statement in a trigger body causes another trigger to be fired, the triggers are said to be cascading. Max = 32.
21.What are mutating triggers ?
A trigger giving a SELECT on the table on which the trigger is written.

22.What are constraining triggers ?
A trigger giving an Insert / Update on a table having referential integrity constraint on the triggering table.

23.Describe Oracle database's physical and logical structure ?
Physical : Data files, Redo Log files, Control file.
Logical : Tables, Views, Tablespaces, etc.

24.Can you increase the size of a tablespace ? How ?
Yes, by adding datafiles to it.

25.Can you increase the size of datafiles ? How ?
No (for Oracle 7.0)Yes (for Oracle 7.3 by using the Resize clause ----- Confirm !!).

26.What is the use of Control files ?
Contains pointers to locations of various data files, redo log files, etc.

27.What is the use of Data Dictionary ?
Used by Oracle to store information about various physical and logical Oracle structures e.g. Tables, Tablespaces, datafiles, etc

28.What are the advantages of clusters ?
Access time reduced for joins.

29.What are the disadvantages of clusters ?
The time for Insert increases.

30.Can Long/Long RAW be clustered ?
31.Can null keys be entered in cluster index, normal index ?

32.Can Check constraint be used for self referential integrity ? How ?
Yes. In the CHECK condition for a column of a table, we can reference some other column of the same table and thus enforce self referential integrity.

33.What are the min. extents allocated to a rollback extent ?

34.What are the states of a rollback segment ? What is the difference between partly available and needs recovery ?
The various states of a rollback segment are :ONLINE, OFFLINE, PARTLY AVAILABLE, NEEDS RECOVERY and INVALID.

35.What is the difference between unique key and primary key ?
Unique key can be null; Primary key cannot be null.

36.An insert statement followed by a create table statement followed by rollback ? Will the rows be inserted ?

37.Can you define multiple savepoints ?

38.Can you Rollback to any savepoint ?

40.What is the maximum no. of columns a table can have ?

Data Warehousing Interview Questions

1) What is source qualifier?
2) Difference between DSS & OLTP?
3) Explain grouped cross tab?
4) Hierarchy of DWH?
5) How many repositories can we create in Informatica?
6) What is surrogate key?
7) What is difference between Mapplet and reusable transformation?
8) What is aggregate awareness?
9) Explain reference cursor?
10) What are parallel querys and query hints?
11) DWH architecture?
12) What are cursors?
13) Advantages of de normalized data?
14) What is operational data source (ODS)?
15) What is meta data and system catalog?
16) What is factless fact schema?
17) What is confirmed dimension?
18) What is the capacity of power cube?
19) Difference between PowerPlay transformer and power play reports?
20) What is IQD file?
21) What is Cognos script editor?
22) What is difference macros and prompts?
23) What is power play plug in?
24) Which kind of index is preferred in DWH?
25) What is hash partition?
26) What is DTM session?
27) How can you define a transformation? What are different types of transformations in Informatica?
28) What is mapplet?
29) What is query panel?
30) What is a look up function? What is default transformation for the look up function?
31) What is difference between a connected look up and unconnected look up?
32) What is staging area?
33) What is data merging, data cleansing and sampling?
34) What is up date strategy and what are th options for update strategy?
35) OLAP architecture?
36) What is subject area?
37) Why do we use DSS database for OLAP tools?
38) What is a universe?
39) Analysis in business objects?
40) Who launches the supervisor product in BO for first time?
41) How can you check the universe?
42) What are universe parameters?
43) Types of universes in business objects?
44) What is security domain in BO?
45) Where will you find the address of repository in BO?
46) What is broad cast agent?
47) In BO 4.1 version what is the alternative name for broadcast agent?
48) What services the broadcast agent offers on the server side?
49) How can you access your repository with different user profiles?
50) How many built-in objects are created in BO repository?
51) What are alertors in BO?
52) What are different types of saving options in web intelligence?
53) What is batch processing in BO?
54) How can you first report in BO by using broadcast agent?
55) Can we take report on Excel in BO?

VB Interview Questions

  • Why do you use Option Explicit?
  • What are the commonly used data types in VBScript?
  • What is a session object?
  • What are the three objects of ADO?
  • What are the lock-types available in ADO?
  • Explain. What are the cursor types available in ADO? Explain.
  • What is a COM component? How do you register a COM component?
  • What is a virtual root and how do you create one?
  • What is a database index, how do you create one, discuss its pros and cons?
  • How do you use multiple record sets(rs.NextRecordSet)?
  • As soon as you fetch a record set, what operations would you perform?
  • Define a transaction.
  • What are ACID properties of a transaction?
  • How would you remotely administer IIS?
  • What is RAID? What is it used for?
  • What is normalization? Explain normalization types.
  • What is the disadvantage of creating an index in every column of a database table?
  • What are the uses of source control software?
  • You have a query that runs slowly, how would you make it better?
  • How would you make it better in .NET environment?
  • What is a bit datatype? What is it used for?
  • How would you go about securing IIS and MS-SQL Server?
  • What is the difference between Request("field") and Request.Form("field")?
  • What versions of VB have you used? Have you also used VBA or VBScript?
  • Have you ever used classes? If so, how have you used them?
  • Have you ever created ActiveX DLLs? If so, why did you create the DLLs instead of using code in the main application?
  • Have you ever created ActiveX controls? If so, what did they do?
  • Have you ever created ActiveX EXEs? If so, what were they used for?
  • Have you ever used Collections? Collection Classes?
  • Have you ever used ADO? DAO? RDO? Any other database engines?
  • What database backends have you worked with? Access? SQL Server? Oracle?
  • Have you ever used resource files? If so, for what reason?
  • Have you used the FileSystemObject? The Dictionary Object? Regular Expressions?
  • Have you developed COM+ components? Any other types of server based components?
  • What source code control systems have you used?
  • What versions of Windows have you used? Have you used any other operating systems?
  • What third party ActiveX controls have you used?
  • Are there any other programming tools, such as database diagramming, UML, or CASE tools, that you've used?
  • Have you developed components for IIS? Developed ASP pages?
  • If you were writing a program, what method would you use to send information from the main form of the application to a modal popup form and then pass any changes to the data back to the main form when the popup form was closed?
  • How would you center a form on the screen? How about centering it on another form?
  • If an event, such as a tool bar button or menu click,occurs on a MDI parent how can it invoke an action on one or more MDI child forms?
  • What are some methods you can use to send data from one VB executable to another one?
  • What are the differences between a standard module and a class module?
  • What do you have to do to make your class visible to programs other than your own?
  • How can you tell what kind of object an object variable is holding?
  • Describe the different scopes of variables in VB.
  • Describe the difference between a public variable in a form and one in a standard code module.
  • How do you handle error conditions in your code?
  • What are some uses and misuses of variants?
  • What are some of the steps you can take to determine why your program is crashing with "Invalid Page Fault" errors?
  • What are the different ways you can use threading in VB? When are they appropriate?
  • How many tabs in a tabbed dialog do you consider appropriate?
  • How many items should you make available to users in a listbox or combo box?
  • What are the three main differences between flexgrid control and dbgrid(Data bound Grid) control
    The Microsoft FlexGrid (MSFlexGrid) control displays and operates on tabular data. It allows complete flexibility to sort, merge, and format tables containing strings and pictures. When bound to a Data control, MSFlexGrid displays read-only data.Adaptation to existing Visual Basic code for the data-bound grid (DBGrid).

    Dbgrid is A spreadsheet-like bound control that displays a series of rows and columns representing records and fields from a Recordset object.

    The data grids are bound controls; that is, they require a data source that actually connects to a database and retrieves their data. And it seems that the root of the problem with DBGrid is that there's no data source that can be readily included along with the DBGrid control.In Visual Basic, the solution is simply to include the Data Control on the same form as DBGrid. But the Data Control is an intrinsic control; it's unavailable to anything outside of the Visual Basic environment itself. and VB 6.0 has a new set of data controls (DataGrid, DataList, DataCombo, MSHFlexGrid, MSFlexGrid) that once again are bound controls. Unlike DBGrid, though, they support OLE DB, and therefore rely on the an ADO Data Source (and in particular the ActiveX Data Objects Data Control, or ADO DC) for data access. Unlike the Data Control, the ADODC is a custom control (that is, an .OCX) that can be added to any project. In short, if you add ADO DC to your project along with theDataGrid control.
  • ActiveX and Types of ActiveX Components in VB ?
    Standard EXE
    ActiveX EXE
    ActiveX DLL
    ActiveX document
    ActiveX Control
  • What is difference between inprocess and out of process ?
    An in-process component is implemented as a DLL, and runs in the same process space as its client app, enabling the most efficient communication between client and component.Each client app that uses the component starts a new instance of it.
    An out of process component is implemented as an EXE, and unlike a dll, runs in its own process space. As a result, exe's are slower then dll'sbecause communications between client and component must be marshalled across process boundaries. A single instance of an out of process component can service many clients.
  • Advantage of ActiveX Dll over Active Exe ?

    ACTIVEX DLL:An in-process component, or ActiveX DLL, runs in another application’s process. In-process components are used by applications or other in-process components. this allows you to wrap up common functionality (like an ActiveX Exe).

    ACTIVEX EXE:An out-of-process component, or ActiveX EXE, runs in its own address space. The client is usually an application running in another process.The code running in an ActiveX Exe is running in a separate process space. You would usually use this in N-Tier programming.

    An ActiveX EXE runs out of process while an ActiveX DLL runs in the same process space as VB app. Also, and ActiveX EXE can be run independent of your application if desired.
  • Explain single thread and multithread thread apartments.
    All components created with Visual Basic use the apartment model, whether they’re single-threaded or multithreaded. A single-threaded component has only one apartment, which contains all the objects the component provides.
    This means that a single-threaded DLL created with Visual Basic is safe to use with a multithreaded client. However, there’s a performance trade-off for this safety. Calls from all client threads except one are marshaled, just as if they were out-of-process calls.
  • What is a Component?
    If you compile an ActiveX dll, it becomes a component.If you compile an ActiveX Control, it becomes both a component and a control.
    Component is a general term used to describe code that's grouped by functionality. More specifically, a component in COM terms is a compiled collection of properties/methods and events.
    Typically a component is loaded into your project via the References whereas an ActiveX Control is loaded into your project via "components".
  • What is meant by "Early Binding" and "Late Binding"? Which is better?
    Early binding and late binding refer to the method used to bind an interface's properties and methods to an object reference (variable). Early binding uses type library information at design time to reference procedures, while late binding handles this at run time. Late bindinghandles this by interrogating the reference before each call to insure that it supports a particular method. Since every call to a late boundobject actually requires two calls ("Do you do this?" followed by "Okay, do it then"), late binding is much less efficient than early binding. Except where early binding is not supported (ASP, scripting, etc.), late binding should only be used in very special cases.
    It is a common misconception that any code using the CreateObject function instead of
    Set = New is using late binding. This is not the case. The type declaration of the object variable determines whetherit is late or early bound, as in the following:

    Dim A As Foo
    Dim B As Foo
    Dim C As Object
    Dim D As Object
    Set A = New Foo 'Early Bound
    Set B = CreateObject("FooLib.Foo") 'Early Bound
    Set C = CreateObject("FooLib.Foo") 'Late Bound
    Set D = New Foo 'Late Bound

HR Interview Questions

1. Tell me about yourself?
I am down-to-earth, sweet, smart, creative, industrious, and thorough.

2. How has your experience prepared you for your career?
Aside from the discipline and engineering foundation learning that I have gained from my courses, I think the design projects, reports, and presentations have prepared me most for my career.
Work Experience:
Through internships, I have gained self-esteem, confidence, and problem-solving skills. I also refined my technical writing and learned to prepare professional documents for clients.
Student Organizations:
By working on multiple projects for different student organizations while keeping up my grades, I've built time management and efficiency skills. Additionally, I've developed leadership, communication, and teamwork abilities.
Life Experience:
In general, life has taught me determination and the importance of maintaining my ethical standards.

3. Describe the ideal job.
Ideally, I would like to work in a fun, warm environment with individuals working independently towards team goals or individual goals. I am not concerned about minor elements, such as dress codes, cubicles, and the level of formality. Most important to me is an atmosphere that fosters attention to quality, honesty, and integrity.

4. What type of supervisor have you found to be the best?
I have been fortunate enough to work under wonderful supervisors who have provided limited supervision, while answering thoughtful questions and guiding learning. In my experience, the best supervisors give positive feedback and tactful criticism.

5. What do you plan to be doing in five years' time?
Taking the Project Management exam and serving in supervisory/leadership roles both at work and in professional/community organization(s).

6. What contributions could you make in this organization that would help you to stand out from other applicants?
In previous internships, my industriousness and ability to teach myself have been valuable assets to the company. My self-teaching abilities will minimize overhead costs, and my industriousness at targeting needs without prompting will set me apart from others. Additionally, one thing that has always set me apart from my scientific/engineering peers are my broad interests and strong writing abilities.

7. What sort of criteria are you using to decide the organization you will work for?
Most importantly, I am looking for a company that values quality, ethics, and teamwork. I would like to work for a company that hires overachievers.

8. What made you choose your major?
My academic interests are broad, so I sought engineering to achieve a great balance of mathematics, chemistry, biology, physics, and writing.

9. Have your university and major met your expectations?
The College at has exceeded my expectations by providing group activities, career resources, individual attention, and professors with genuine interest in teaching.
My major has met my expectations by about 90%. I would have enjoyed more choices in courses, and would have preferred more calculus-based learning.

10. What made you choose this college?
I chose this college for the following reasons: The High standards of learning and the excellent faculty impressed me, I saw active student groups, and the people were very friendly.

11. List 2-3 of your greatest achievements since you've been in college and why?
Receiving the Meritorious Student Award and Outstanding Achievement Award in organizing the National Level Event.
I got involved with student activities to overcome my debilitating shyness. Receiving these awards signified that I had accomplished a transition from dragging myself to participate to feeling energized by it.
Earning the highest grade in class of ~200 people, I worked very hard for this grade, so it was a great feeling to see that the hard work paid off.

12. Which subjects have you enjoyed studying the most and why?
I have enjoyed software engineering, programming in C, Datastructure and DBMS because I love the topics, where I can put my creativity logically.
Calculus and linear algebra also excite me because I love logic.
MIS thrilled me because I have a strong interest in organizing the things logically.

13. Which subjects did you dislike and why?
Introductory Accounting little interest in me, most likely because I am not very good at numbers, the book was ineffective, and I had little spare time that semester to look into other resources.

14. Do you have plans to continue your education?
Yes, but not immediately. I plan to continue with either part time or distance learning MBA depending on which will be more beneficial to my work.

15. How would a professor who knows you well describe you? One who does not know you well?
A professor who knows me well would likely describe my personal qualities: sweet, down-to-earth, smart, hard-working, and conscientious.
As specific examples of those who did not know me well, my accounts professor considered me smart and respectful, and thought that I must have enjoyed the class a lot, due to my performance.

16. Given the chance, how would you alter your education?
Knowing now what I like the most, I would have used my electives for extra math and psychology classes, since I tend to be well-rounded enough that a variety of classes are unnecessary; my personal reading is diverse enough. I have found that mathematics and psychology are helpful to all career and life paths.

17. Which part-time job did you enjoy the most and why?
Working for was most enjoyable to me, since I felt like I was significantly contributing to the company, and I enjoyed learning on my own.

18. Interests:
Some of my interests include Music, singing, writing, reading (especially novels) , drawing, watching cricket, and computers.

19. What are your strengths?
My strongest strength is the ability to teach myself difficult material, regardless of the subject. Additionally, I have always excelled verbally and look forward to writing opportunities.

20. What are your weaknesses?
I tend to try to do too many things, leaving little time for myself. I have worked on balancing myself for the last several months. I am also working on improving my public speaking skills.

21. What sort of serious problems have you experienced, and how have you handled them?
Getting caught with Typhoid jsut a month before my Semester Exams was the very hard and serious issue but fortunately, I had studied throughout the semester. I missed about 15 days of college due to the illness. Within 2 weeks, I had recovered reasonably from the illness and thanks to my habit of making notes, which proved very beneficial at the time of exams.

22. Do you or have you in the past experimented with illegal drugs?
No. My only addictions are caffeine and sugar.

23. Would you be willing to take a drug test?
Of course.

24. Do you drink alcohol socially?
No, but I enjoy Shirley Temples quite a bit.

25. How do you propose to compensate for your lack of experience?
My zeal, fast learning and quick adaption to the technogies will be an added advantage for the job I would be doing. I am hard-worker and a very quick learner and never afraid to put an extra effort to reach the desired level required by the job.

Some of the questions posted by many college freshers

  • I have given an HR inteview where they ask me to write where do you see yourself in 5 years down lane.
  • Why should we not hire you?
  • What should be the answer for why did you choose and persue carrer in only hr in an interview
  • What to answer and what not to answer for "Tell me something about you"
  • Why do you want to leave your current job?
  • Why do you want to join in industry? (for recent graduates)
  • How do you organize your priorities?
  • What is management interview ? (after clearing technical interview they asked me to come for this?)
  • What are the things you are suppose to describe, if the HR asks you "Tell me something about yourself
  • How can I elobrate my strengths with examples?
  • What are the competitive challenges in Human Resource Management?
  • Why u want to change the present company?
  • What is ergonomics
  • Why do you want to join this company?
  • Why do you want to leave your previous job?
  • where do you see yourself after 10 years from now?
  • Suppose you already have job offer and giving to interview to other new company. What reasoning should you give for sitting again?
  • My questions are:-Why do you like to join this company?What would you do for the growth of this company?
  • What should i answer if my interviewer asks me about my short and long term goals.Tell me with some example.
  • Give an answer with an example how i should answer for tell me about yourself?
  • If they ask tell about yourself,from where i have to start.give an answer with an example?
  • Why do you think you would do well at this job?
  • What is more important to you: the money or the work?
  • What would your previous supervisor say your strongest point is?
  • Tell me about a problem you had with your supervisor.
  • What has disappointed you about a job?
  • Tell me about your ability to work under pressure.
  • Do your skills match this job or another job more closely?
  • What motivates you to do your best on the job?
  • Are you willing to work overtime? Nights? Weekends?
  • Would you be willing to relocate if required?
  • Are you willing to put the interests of the organization ahead of your own?
  • Describe your management style.
  • What have you learned from mistakes on the job?
  • Do you have any blind spots?
  • If you were hiring a person for this job, what would you look for?
  • Do you think you are overqualified for this position?
  • How do you propose to compensate for your lack of experience?
  • What qualities do you look for in a boss?
  • Tell me about a time when you helped resolve a dispute between others.

Monday, November 26, 2007

PHP Interview Questions - Part 4

1What is PHP?

PHP Version 3.0 is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly.

2 What is its relation to PHP/FI?

PHP is the successor to PHP/FI 2.0.

3 Can I run both PHP/FI 2.0 and PHP at the same time?

Yes, PHP was written so as to not interfere with an existing PHP/FI 2 installation. Instructions for building Apache 1.3.0 with both PHP/FI 2 and PHP modules can be found HERE. A different spin on this is HERE, although the first step where the PHP2 regex code is substituted with the PHP regex code seems redundant. The two regex dirs are pretty much identical.

4 What are the differences between PHP and PHP/FI 2.0?

For a complete list of the changes, read the CHANGES file included in the PHP distribution. Some highlights:

· All-new parser.

· Persistent database connections.

· A native Windows95/NT port.

· IMAP, SNMP, and LDAP extensions.

5 I heard it's possible to access Microsoft SQL Server from PHP. How?

On Windows 95/NT machines, you can simply use the included ODBC support and the correct ODBC driver.

A copy of step-by-step ODBC setup can be found here.

On Unix machines, you can use the Sybase-CT driver to access Microsoft SQL Servers because they are (at least mostly) protocol-compatible. Sybase has made a free version of the necessary libraries for Linux systems. For other Unix operating systems, you need to contact Sybase for the correct libraries. Also see the answer to the next question - 1.6.

6 Can I access Microsoft Access databases?

Yes. You already have all the tools you need if you are running entirely under Windows 95/98 or NT, where you can use ODBC and Microsoft's ODBC drivers for Microsoft Access databases.

If you are running PHP on a Unix box and want to talk to MS-Access on a Windows box you will need Unix ODBC drivers. OpenLink Software has Unix-based ODBC drivers that can do this. There is a free pilot program where you can download an evaluation copy that doesn't expire and prices start at $675 for the commercial supported version.

Another alternative is to use an SQL server that has Windows ODBC drivers and use that to store the data, which you can then access from Microsoft Access (using ODBC) and PHP (using the built-in drivers), or to use an intermediary file format that Access and PHP both understand, such as flat-files or dBase databases. On this point Tim Hayes from OpenLink software writes:

Using another database as an intermediary is not a good idea, when you can use ODBC from PHP straight to your database - i.e. with OpenLink's drivers. If you do need to use an intermediary file format, OpenLink have now released Virtuoso (a virtual database engine) for NT, Linux and other unix platforms. Please visit our website for a free download.

One option that has proven successful is to use MySQL and its MyODBC drivers on Windows and synchronizing the databases. Steve Lawrence writes:

1. Install MySQL on your platform according to instructions with MySQL. Latest available from (get it from your mirror!). No special configuration required except when you set up a database, and configure the user account, you should put % in the host field, or the host name of the Windows computer you wish to access MySQL with. Make a note of your server name, username, and password.

2. Download the MyODBC for Windows driver from the MySQL site. Latest release is (NT available too, as well as source code). Install it on your Windows machine. You can test the operation with the utilities included with this program.

3. Create a user or system dsn in your ODBC administrator, located in the control panel. Make up a dsn name, enter your hostname, user name, password, port, etc for you MySQL database configured in step 1.

4. Install Access with a full install, this makes sure you get the proper add-ins.. at the least you will need ODBC support and the linked table manager.

5. Now the fun part! Create a new access database. In the table window right click and select Link Tables, or under the file menu option, select Get External Data and then Link Tables. When the file browser box comes up, select files of type: ODBC. Select System dsn and the name of your dsn created in step 3. Select the table to link, press ok, and presto! you can now open the table and add/delete/edit data on your MySQL server! You can also build queries, import/export tables to MySQL, build forms and reports, etc.

Tips and Tricks: - You can construct your tables in access and export them to MySQL, then link them back in. That makes table creation quick.
- When creating tables in access, you must have a primary key defined in order to have write access to the table in access. Make sure you create a primary key in MySQL before linking in access.
- If you change a table in MySQL, you have to re-link it in access. Go to tools>add-ins>linked table manager, cruise to your ODBC DSN, and select the table to re-link from there. you can also move your dsn source around there, just hit the always prompt for new location checkbox before pressing ok.

7 Is there a PHP mailing list?

Of course! To subscribe, send mail to You don't need to include anything special in the subject or body of the message.

To unsubscribe, send mail to

8 Help! I can't seem to subscribe to the mailing list!

Help! I can't seem to unsubscribe from the mailing list!

If you have problems subscribing to or unsubscribing from the PHP mailng list, it may be because the mailing list software can't figure out the correct mailing address to use. If your email address was, you can send your subscription request to, or your unsubscription request to

9 Is there an archive of the mailing list anywhere?

Yes, you will find a list of archive sites on the Support page.

10 How did you do those pop-out windows for the Search and Mirror buttons?

Our site designer, Colin Viebrock (, says:

Those fancy pop-out layers are done with Dynamic HTML (DHTML), Cascading Style Sheets (CSS) and Javascript (version 1.2).

There are plenty of references on the web about DHTML and CSS, including:

· CSS Level 1 Spec:

· Macromedia's DHTML Zone:

· Webreference's DHTML Lab:

· Guide to Cascading Style Sheets:

· Dynamic Duo - Cross-Browser DHTML:

· Netscape's Guide to JS 1.2:

But your best source of information is to view the source code to the pages on the PHP site. To see the actual DHTML/Javascript code, use your browser's "View Source" function. To see how this code was generated dynamically using PHP, click on the "Source" button in the upper-right corner of any PHP page. You will probably also want to view the source of the "" file - there is a link to it at the bottom of every source page.

11 Can I access Empress RDBMS databases?

Yes. PHP 3.0.6 and Empress RDBMS v8.10 and higher are compatible.

You already have all the tools you need if you are running entirely under Windows 95/98 or NT, where you can use ODBC and the Empress ODBC driver for Windows.

If you are running PHP on a Unix box and want to access Empress databases, you can link the Empress ODBC client driver directly into the PHP unified ODBC API.
Note that does NOT make PHP an ODBC client. The unified ODBC interface simplies uses the ODBC application program interface (API).

Because Empress uses the PHP unified ODBC interface it has very little explicit Empress specific syntax. It is of course possible to use Empress specific SQL in the SQL statements themselves, but this does not affect the interface. It is a good general policy to stick to ANSI standard SQL whenever possible.

Empress Specifics: The only item which is specific to Empress in PHP is that there are two methods for specifying the DNS in the odbc_connect ()odbc_pconnect () functions. The connect syntax is: and

odbc_connect (dsn, user_id, password)

odbc_pconnect (dsn, user_id, password)

For Empress dsn can be specified as either:

Data source name

This is the logical database name specified in the ODBC.INI file.

A full connection string, as specified in the ODBC standard.


Note that there are other options for this string. But the three shown above are the most important for use with PHP.

Which of these you use is up to you. There are advantages and disadvantages to both. Using the full connection string means that you do NOT require an ODBC.INI file to access the database. However, if you move the datasource, or change the port on which the RDBMS server listens, you will have to modify every call to the odbc_connect/pconnect function.
The choice is yours...

Empress Installation: In order to add the Empress interface to PHP you require an Empress RDBMS with the Empress Connectivity option. If your PHP installation is on the same platform as the RDBMS then setting EMPRESS_PATH to the installation directory will automatically locate the Empress ODBC client driver. However, if the PHP installation is on a separate platform from the RDBMS you will also require an ODBC client on that platform, and you will need to specify the location of the driver when configuring the PHP installation.

2. Obtaining PHP

1 Where can I obtain PHP?

You can download PHP from any of the members of the PHP network of sites. These can be found at You can also use anonymous CVS to get the absolute latest version of the source. For more information, go to

2 Are pre-compiled binary versions available?

Yes, although they are not always up to date. The Windows binary is generally current, but the Unix binaries lag behind and are only available for certain platforms. All download are available in the Downloads section.

3 Where can I get libraries needed to compile some of the optional PHP extensions?

Note: Those marked with * are not thread-safe libraries, and should not be used with PHP as a server module in the multi-threaded Windows web servers (IIS, Netscape). This does not matter in Unix environments, yet.

· LDAP (unix):

· LDAP* (unix):

· LDAP (unix/win): Netscape Directory (LDAP) SDK 1.1 There is also a free LDAP server at:

· Berkeley DB2 (Unix/Win):

· SNMP* (Unix): (Note: PHP uses the native SNMP interface in Windows.)

· GD* (Unix/Win):

· mSQL* (Unix):

· mSQL* (Win) : MSQL PC Home Page

· MySQL (Unix):

· IMAP* (Win/Unix):

· Sybase-CT* (Linux, libc5): Available locally

· FreeType (libttf):

· ZLib (Unix/Win32):

· expat XML parser (Unix/Win32):

· PDFLib:

· mcrypt:

· mhash:

· t1lib:

· dmalloc:

· aspell:

· Readline:

4 How do I get these libraries to work?

You will need to follow instructions provided with the library. Some of these libraries are detected automatically when you run the 'configure' script of PHP (such as the GD library), and others you will have to enable using '--with-EXTENSION' options to 'configure'. Run 'configure --help' for a listing of these.

5 I got the latest version of the PHP source code from the CVS repository on my Windows 95/NT machine, what do I need to compile it?

First, you will need Microsoft Visual C++ v6 (v5 may do it also, but we do it with v6), and you will need to download the support files. You will need to unzip this file (which has subdirectories, so make sure your unzip program keeps them) into the win32 subdirectory of the source distribution.

6 Where do I find the Browser Capabilities File?

You can find PHP's own browscap.ini file at There is also another browscap.ini file at

3. Installation

To install PHP, follow the instructions in the INSTALL file located in the distribution. Windows 95 and NT users should also read the README.WIN32 file. There are also some helpful hints for Windows users here.

If you are trying to install PHP for use with Netscape's web server on Unix see:

1 Where should my php3.ini file be located?

By default on UNIX it should be in /usr/local/lib. Most people will want to change this at compile-time with the --with-config-file-path flag. You would, for example, set it to something like:


And then you would copy php3.ini-dist from the distribution to /etc/php3.ini and edit it to make any local changes you want.

2 I installed PHP using RPMS, but Apache isn't processing the PHP pages! What's going on here?

· Assuming you installed Apache PHP completely with RPMS, you need to uncomment or add some or all of the following lines in your http.conf file:
# Extra Modules
AddModule mod_php.c
AddModule mod_php3.c
AddModule mod_perl.c
# Extra Modules
LoadModule php_module modules/
LoadModule php3_module modules/
LoadModule perl_module modules/

· And add:
AddType application/x-httpd-php3 .php3
To the global properties, or to the properties of the VirtualDomain you want to have PHP support added to.

3 I installed PHP using RPMS, but it doesn't compile with the database support I need! What's going on here?

Due to the way PHP is currently built, it is not easy to build a complete flexible PHP RPM. This issue will be addressed in PHP4. For PHP, we currently suggest you use the mechanism described in the INSTALL.REDHAT file in the PHP distribution. If you insist on using an RPM version of PHP, read on...
Currently the RPM packagers are setting up the RPMS to install without database support to simplify installations AND because RPMS use /usr/ instead of the standard /usr/local/ directory for files. You need to tell the RPM spec file which databases to support and the location of the top-level
This example will explain the process of adding support for the popular MySQL database server, using the mod installation for Apache.
Of course all of this information can be adjusted for any database server that PHP supports. I will assume you installed MySQL and Apache completely with RPMS for this example as well.
of your database server.

· First remove mod_php3
rpm -e mod_php3

· Then get the source rpm and INSTALL it, NOT --rebuild
rpm -Uvh mod_php3-3.0.5-2.src.rpm

· Then edit the /usr/src/redhat/SPECS/mod_php3.spec file
In the %build section add the database support you want, and the path.
For MySQL you would add --with-mysql=/usr \
The %build section will look something like this:
./configure --prefix=/usr \
--with-apxs=/usr/sbin/apxs \
--with-config-file-path=/usr/lib \
--enable-debug=no \
--enable-safe-mode \
--with-exec-dir=/usr/bin \
--with-mysql=/usr \

· Once this modification is made then build the binary rpm as follows:
rpm -bb /usr/src/redhat/SPECS/mod_php3.spec

· Then install the rpm
rpm -ivh /usr/src/redhat/RPMS/i386/mod_php3-3.0.5-2.i386.rpm

Make sure you restart Apache, and you now have PHP with MySQL support using RPM's. Note that it is probably much easier to just build from the distribution tarball of PHP and follow the instructions in INSTALL.REDHAT found in that distribution.

4. Build Problems

1 I got the latest version of PHP using the anonymous CVS service, but there's no configure script!

You have to have the GNU autoconf package installed so you can generate the configure script from Just run make -f in the top-level directory after getting the sources from the CVS server. (Also, unless you run configure with the --enable-maintainer-mode option, the configure script will not automatically get rebuilt when the file is updated, so you should make sure to do that manually when you notice has changed. One symptom of this is finding things like @VARIABLE@ in your Makefile after configure or config.status is run.)

2 I'm having problems configuring PHP to work with Apache. It says it can't find httpd.h, but it's right where I said it is!

You need to tell the configure/setup script the location of the top-level of your Apache source tree. This means that you want to specify '--with-apache=/path/to/apache' and not '--with-apache=/path/to/apache/src'.

3 When I run configure, it says that it can't find the include files or library for GD, gdbm, or some other package!

You can make the configure script looks for header files and libraries in non-standard locations by specifying additional flags to pass to the C preprocessor and linker, such as:

    CPPFLAGS=-I/path/to/include LDFLAGS=-L/path/to/library ./configure

If you're using a csh-variant for your login shell (why?), it would be:

    env CPPFLAGS=-I/path/to/include LDFLAGS=-L/path/to/library ./configure

4 When it is compiling the file, it gives me errors that say 'yytname undeclared'.

You need to update your version of Bison. You can find the latest version at

5 When I run 'make', it seems to run fine but then fails when it tries to link the final application complaining that it can't find some files.

Some old versions of make that don't correctly put the compiled versions of the files in the functions directory into that same directory. Try running "cp *.o functions" and then re-running 'make' to see if that helps. If it does, you should really upgrade to a recent version of GNU make.

6 When linking PHP, it complains about a number of undefined references.

Take a look at the link line and make sure that all of the appropriate libraries are being included at the end. Common ones that you might have missed are '-ldl' and any libraries required for any database support you included.

If you're linking with Apache 1.2.x, did you remember to add the appropriate information to the EXTRA_LIBS line of the Configuration file and re-rerun Apache's Configure script? See the INSTALL file that comes with the distribution for more information.

Some people have also reported that they had to add '-ldl' immediately following 'libphp3.a' when linking with Apache.

7 I can't figure out how to build PHP with Apache 1.3.

This is actually quite easy. Follow these steps carefully:

· Grab the latest Apache 1.3 distribution from

· Ungzip and untar it somewhere, for example /usr/local/src/apache-1.3.

· Compile PHP by first running ./configure --with-apache=//apache-1.3 (substitute for the actual path to your apache-1.3 directory.

· Type 'make' followed by 'make install' to build PHP and copy the necessary files to the Apache distribution tree.

· Change directories into to your //apache-1.3/src directory and edit the Configuration file. At the end of the file, add: AddModule modules/php3/libphp3.a.

· Type: './Configure' followed by 'make'.

· You should now have a PHP-enabled httpd binary!

Note: You can also use the new Apache ./configure script. See the instructions in the README.configure file which is part of your Apache distribution. Also have a look at the INSTALL file in the PHP distribution.

8 I have followed all the steps to install the Apache module version on UNIX, and my PHP scripts show up in my browser or I am being asked to save the file. Help!

This means that the PHP module is not getting invoked for some reason. Three things to check before asking for further help:

· Make sure that the httpd binary you are running is the actual new httpd binary you just built. To do this, try running: /path/to/binary/httpd -l
If you don't see mod_php3.c listed then you are not running the right binary. Find and install the correct binary.

· Make sure you have added the correct Mime Type to one of your Apache .conf files. It should be: AddType application/x-httpd-php3 .php3
Also make sure that this AddType line is not hidden away inside a or block which would prevent it from applying to the location of your test script.

· Finally, the default location of the Apache configuration files changed between Apache 1.2 and Apache 1.3. You should check to make sure that the configuration file you are adding the AddType line to is actually being read. You can put an obvious syntax error into your httpd.conf file or some other obvious change that will tell you if the file is being read correctly.

9 It says to use: --activate-module=src/modules/php3/libphp3.a, but that file doesn't exist, so I changed it to --activate-module=src/modules/php3/libmodphp3.a and it doesn't work!? What's going on?

Well, you decided to try to outsmart the people who wrote those nice step-by-step instructions for you and you have now discovered that these people cannot be outsmarted. The libphp3.a file is not supposed to exist. The Apache build process will create it.

10 When I try to build Apache with PHP as a static module using --activate-module=src/modules/php3/libphp3.a it tells me that my compiler is not ANSI compliant.

This is a crappy error message and has been fixed in Apache-1.3.10 (not available yet). For now, go and edit the src/Configure file in the Apache source directory and down around line 2140 you will find a line that looks like this:

if ./helpers/TestCompile sanity; then

Change this line to be this:

if ./helpers/TestCompile -v sanity; then

and now re-run the Apache configure script. It will now show you the actual errors that caused your build to fail. It is usually due to a missing library.

11 When I try to build PHP using --with-apxs I get strange error messages

There are two things to check here. First, for some reason when Apache builds the apxs Perl script, it sometimes ends up getting built without the proper compiler and flags variables. Edit your apxs (sometimes found in /usr/local/apache/bin/apxs or /usr/sbin/apxs) and check for these lines:

my $CFG_CFLAGS_SHLIB  = ' ';      # substituted via Makefile.tmpl
my $CFG_LD_SHLIB      = ' ';          # substituted via Makefile.tmpl
my $CFG_LDFLAGS_SHLIB = ' ';      # substituted via Makefile.tmpl

If this is what you see, you have found your problem. Change these lines to say:

my $CFG_CFLAGS_SHLIB  = '-fpic -DSHARED_MODULE';      # substituted via Makefile.tmpl
my $CFG_LD_SHLIB      = 'gcc';          # substituted via Makefile.tmpl
my $CFG_LDFLAGS_SHLIB = q(-shared);# substituted via Makefile.tmpl 

The second possible problem should only be an issue on RedHat-6.1. The apxs script RedHat ships is broken. Look for this line:

my $CFG_LIBEXECDIR    = 'modules';        # substituted via APACI install

If you see the above line, change it to this:

my $CFG_LIBEXECDIR    = '/usr/lib/apache';        # substituted via APACI install

5. Using PHP

1 I would like to write a generic PHP script that can handle data coming from any form. How do I know which POST method variables are available?

Make sure that the track_vars feature is enabled in your php3.ini file. If you compiled PHP with "--enable-track-vars" it will be on by default. Alternatively you can enable it at run-time on a per-script basis by putting at the top of your file. When track_vars is on, it creates three associative arrays. $HTTP_GET_VARS, $HTTP_POST_VARS and $HTTP_COOKIE_VARS. So, to write a generic script to handle POST method variables you would need something similar to the following:

    while (list($var, $value) = each($HTTP_POST_VARS)) {
        echo "$var = $value

2 I need to convert all single-quotes (') to a backslash followed by a single-quote. How can I do this with a regular expression?

First off, take a look at the addslashes() function. It will do exactly what you want. You should also have a look at the magic_quotes_gpc directive in your php3.ini file.

The ereg_replace magic you're looking for, however, is simply:

    $escaped = ereg_replace("'", "\\'", $input);

3 When I do the following, the output is printed in the wrong order:

      function myfunc($argument) {
        echo $argument + 10;
      $variable = 10;
      echo "myfunc($variable) = " . myfunc($variable);

What's going on?

To be able to use the results of your function in an expression (such as concatenating it with other strings in the example above), you need to return the value, not echo it.

4 Hey, what happened to my newlines in:


In PHP, the ending for a block of code is either "?>" or "?>\n" (where \n means a newline). This means that you need to insert an extra newline after each block of PHP code in the above example.

Why does PHP do this? Because when formatting normal HTML, this usually makes your life easier because you don't want that newline, but you'd have to create extremely long lines or otherwise make the raw page source unreadable to achieve that effect.

5 I need to access information in the request header directly. How can I do this?

The getallheaders() function will do this if you are running PHP as a module. So, the following bit of code will show you all the request headers:

    $headers = getallheaders();
  for(reset($headers); $key = key($headers); next($headers)) {
        echo "headers[$key] = ".$headers[$key]."

6 When I try to use authentication with IIS I get 'No Input file specified'

The security model of IIS is at fault here. This is a problem common to all CGI programs running under IIS. A workaround is to create a plain HTML file (not parsed by php) as the entry page into an authenticated directory. Then use a META tag to redirect to the PHP page, or have a link to the PHP page. PHP will then recognize the authentication correctly. When the ISAPI module is ready, this will no longer be a problem. This should not effect other NT web servers. For more information, see:

7 I've followed all the instructions, but still can't get PHP and IIS to work together!

Make sure any user who needs to run a PHP script has the rights to run php.exe! IIS uses an anonymous user which is added at the time IIS is installed. This user needs rights to php.exe. Also, any authenticated user will also need rights to execute php.exe. And for IIS4 you need to tell it that PHP is a script engine.

8 My PHP script works on IE and Lynx, but on Netscape some of my output is missing. When I do a "View Source" I see the content in IE but not in Netscape. Even when I telnet to port 80 directly the correct content shows up. How can this be? PHP is server-side and my browser can't possibly know that the content it is seeing is generated by PHP, so what is going on?

Very good question! ;) This is a tricky little issue and it has come up twice in the past month as of this writing. Both times I ended up spending a good 20 minutes trying to figure out what the heck was going on. The answer is that both IE and Lynx ignore any NULs (\0) in the HTML stream. Netscape does not. The best way to check for this is to compile the command-line version of PHP (also known as the CGI version) and run your script from the command line and pipe it through 'od -c' and look for any \0 characters. (If you are on Windows you need to find an editor or some other program that lets you look at binary files) When Netscape sees a NUL in a file it will typically not output anything else on that line whereas both IE and Lynx will. If this issue has bitten you, congratulations! You are not alone.

9 How do I get all the results from a SELECT MULTIPLE HTML tag?

The SELECT MULTIPLE tag in an HTML construct allows users to select multiple items from a list. These items are then passed to the action handler for the form. The problem is that they are all passed with the same widget name. ie.


This tells PHP to treat var as an array and each assignment of a value to var[] adds an item to the array. The first item becomes $var[0], the next $var[1], etc. The count() function can be used to determine how many options were selected, and the sort() function can be used to sort the option array if necessary.

Note that if you are using JavaScript the [] on the element name might cause you problems when you try to refer to the element by name. Use it's numerical form element id instead, or enclose the variable name in single quotes and use that as the index to the elements array, for example:

   variable = documents.forms[0].elements['var[]'];

10 How am I supposed to mix XML and PHP? It complains about my tags!

You need to turn off the short tags by setting short_tags to 0 in your php3.ini file, or by using the php3_short_tags Apache directive. (You could even use a section to do this selectively.) You can also disable and re-enable the short tags in your script using the short_tags() function.

11 How can I use PHP with FrontPage or Dreamweaver or some other HTML editor that insists on moving my code around?

One of the easiest things to do is to enable using ASP tags in your PHP code. This allows you to use the ASP-style <% and %> code delimiters. Most of the popular HTML editors handle those more intelligently (for now). To enable the ASP-style tags, you need to set the asp_tags php3.ini variable, or use the php3_asp_tags Apache directive.

12 Where can I find a complete list of pre-set variables available to me, and why are these not documented in the PHP documentation?

The best way is to stick a tag on a page and load it up. This will show you all sorts of information about your PHP setup, including a list of both environment variables and also special variables set by your web server. This list can't really be documented in the PHP documentation because it will change from one server to another.

13 Why do I always get an error that looks something like this:
Warning: 0 is not a MySQL result index in file on line 8
What am I doing wrong?

You are trying to use a result identifier that is 0. The 0 indicates that your query failed for some reason. You need to check for errors after submitting a query and before you attempt to use the returned result identifier. The proper way to do this is with code similar to the following:

        $result = mysql_query("select * from tables_priv");
        if(!$result) {
            echo mysql_error();


        $result = mysql_query("select * from tables_priv") 
                    or die("Bad query: ".mysql_error());

14 I'm trying to use an tag, but the $foo.x and $foo.y variables aren't available. Where are they?

When submitting a form, it is possible to use an image instead of the standard submit button with a tag like:


When the user clicks somewhere on the image, the accompanying form will be transmitted to the server with two additional variables: foo.x and foo.y.

Because $foo.x and $foo.y are invalid variable names in PHP, they are automagically converted to $foo_x and $foo_y. That is, the periods are replaced with underscores.

6. New Features

1 I saw PHP offers persistent database connections. What does that mean?

Persistent connections are SQL links that do not close when the execution of your script ends. When a persistent connection is requested, PHP checks if there's already an identical persistent connection (that remained open from earlier) - and if it exists, it uses it. If it does not exist, it creates the link. An 'identical' connection is a connection that was opened to the same host, with the same username and the same password (where applicable).

People who aren't thoroughly familiar with the way web servers work and distribute the load may mistake persistent connects for what they're not. In particular, they do not give you an ability to open 'user sessions' on the same SQL link, they do not give you an ability to build up a transaction efficently, and they don't do a whole lot of other things. In fact, to be extremely clear about the subject, persistent connections don't give you any functionality that wasn't possible with their non-persistent brothers.


This has to do with the way web servers work. There are three ways in which your web server can utilize PHP to generate web pages.

The first method is to use PHP as a CGI "wrapper". When run this way, an instance of the PHP interpreter is created and destroyed for every page request (for a PHP page) to your web server. Because it is destroyed after every request, any resources that it acquires (such as a link to an SQL database server) are closed when it is destroyed. In this case, you do not gain anything from trying to use persistent connections -- they simply don't persist.

The second, and most popular, method is to run PHP as a module in a multiprocess web server, which currently only includes Apache. A multiprocess server typically has one process (the parent) which coordinates a set of processes (its children) who actually do the work of serving up web pages. When each request comes in from a a client, it is handed off to one of the children that is not already serving another client. This means that when the same client makes a second request to the server, it may be serviced by a different child process than the first time. What a persistent connection does for you in this case it make it so each child process only needs to connect to your SQL server the first time that it serves a page that makes us of such a connection. When another page then requires a connection to the SQL server, it can reuse the connection that child established earlier.

The last method is to use PHP as a plug-in for a multithreaded web server. Currently this is only theoretical -- PHP does not yet work as a plug-in for any multithreaded web servers. Work is progressing on support for ISAPI, WSAPI, and NSAPI (on Windows), which will all allow PHP to be used as a plug-in on multithreaded servers like Netscape FastTrack, Microsoft's Internet Information Server (IIS), and O'Reilly's WebSite Pro. When this happens, the behavior will be essentially the same as for the multiprocess model described before.

If persistent connections don't have any added functionality, what are they good for?

The answer here is extremely simple -- efficiency. Persistent connections are good if the overhead to create a link to your SQL server is high. Whether or not this overhead is really high depends on many factors. Like, what kind of database it is, whether or not it sits on the same computer on which your web server sits, how loaded the machine the SQL server sits on is and so forth. The bottom line is that if that connection overhead is high, persistent connections help you considerably. They cause the child process to simply connect only once for its entire lifespan, instead of every time it processes a page that requires connecting to the SQL server. This means that for every child that opened a persistent connection will have its own open persistent connection to the server. For example, if you had 20 different child processes that ran a script that made a persistent connection to your SQL server, you'd have 20 different connections to the SQL server, one from each child.

An important summary. Persistent connections were designed to have one-to-one mapping to regular connections. That means that you should always be able to replace persistent connections with non-persistent connections, and it won't change the way your script behaves. It may (and probably will) change the efficiency of the script, but not its behavior!

7. Common Problems

1 I installed PHP, but every time I load a document, I get the message 'Document Contains No Data'! What's going on here?

This probably means that PHP is having some sort of problem and is core-dumping. Look in your server error log to see if this is the case, and then try to reproduce the problem with a small test case. If you know how to use 'gdb', it is very helpful when you can provide a backtrace with your bug report to help the developers pinpoint the problem. If you are using PHP as an Apache module try something like:

· Stop your httpd processes

· gdb httpd

· > run -X -f /path/to/httpd.conf

· Then fetch the URL causing the problem with your browser

· If you are getting a core dump, gdb should inform you of this now

· type: bt

· Send the resulting backtrace to

If your script uses the regular expression functions (ereg() and friends), you should make sure that you compiled PHP and Apache with the same regular expression package. (This should happen automatically with PHP and Apache 1.3.x)

2 I'm trying to access one of the standard CGI variables (such as $DOCUMENT_ROOT or $HTTP_REFERER) in a user-defined function, and it can't seem to find it. What's wrong?

Environment variables are now normal global variables, so you must either declare them as global variables in your function (by using "global $DOCUMENT_ROOT;", for example) or by using the global variable array (ie, "$GLOBALS["DOCUMENT_ROOT"]".

3 I patched Apache with the FrontPage extensions patch, and suddenly PHP stopped working. Is PHP incompatible with the Apache FrontPage extensions?

No, PHP works fine with the FrontPage extensions. The problem is that the FrontPage patch modifies several Apache structures, that PHP relies on. Recompiling PHP (using 'make clean ; make') after the FP patch is applied would solve the problem.

4 I think I found a bug! Who should I tell?

You should go to the PHP Bug Database and make sure the bug isn't a known bug. If you don't see it in the database, use the reporting form to report the bug. It is important to use the bug database instead of just sending an email to one of the mailing lists because the bug will have a tracking number assigned and it will then be possible for you to go back later and check on the status of the bug. The bug database can be found at

8. Migrating from PHP2 to PHP3

1 When I add two strings together and then echo it, it echoes zero instead of the concatenation of the two strings! What's going on? Wouldn't it be great if adding two strings just concatenated them together?

PHP3 does not support the overloading of the addition operator for strings because values that arrive via the GET and POST methods and from databases are always stored as strings. This means that if the plus operator were overloaded to concatenate strings, you could add what you thought were two numbers and get the wrong result! (For example, "4" + "5" would be equal to "45".) One way around this would be to explicitly type-cast one or both of the operands, which is what PHP/FI 2 did.

This has been simplified in PHP3 by the addition of a real string concatenation operator. If you want to "add" two strings together, just write it like: "this" . "that" which will result in the string "thisthat".

The answer to the final part of the question is an emphatic no. Operator overloading can be a source of great confusion, especially when variables aren't very strongly typed to begin with, as they are in PHP3.

2 When I use the chmod(), umask(), or mkdir() functions, the permissions are wrong!

Unlike PHP/FI 2, PHP3 does not interpret the numeric arguments for these functions any differently than for any other function, which means you need to pass in an octal value if you are specifying an octal number, such as:

        chmod($myfile, 0600);


        chmod($myfile, 600);

3 I converted my script from PHP/FI 2.0 to PHP3 syntax, but now it just hangs! When I looked at the processes running on my server, there was one process that was chewing up all of the CPU cycles!

You probably missed the semi-colon on a while (condition); statement. This will cause PHP3 to spin out of control because it is simply executing an empty body for your while loop! Change the semi-colon to a colon and it should work correctly.

4 My user-functions don't work any more! I get a "Parse error (expecting '('" on the first line of the function.

PHP3's function declaration now resembles C function declarations, so your function should look like:

        function printsum($a, $b) {
           echo $a + $b;

You can also use old-style function declarations by use the 'old_function' designation, like so:

        old_function printsum $a, $b (
           echo $a + $b;

5 What happened to the securevar() function that was in PHP2? How can I make sure that a GET-method variable does not overwrite a POST-method one?

The securevar() function in PHP2 was a badly named function. It gave the impression that when used the POST-method was secure. It is not. It is only slightly more difficult to fake POST-method variables than GET-method ones.

There are a couple of ways to achieve similar things in PHP3. The most straightforward way is to do it manually by using the $HTTP_POST_VARSFAQ question 5.1 for instructions on how to enable it. To make sure that $foo, for example, comes from the POST data and nowhere else you would do: array. See

         $foo = $HTTP_POST_VARS["foo"];

A second way to do this is to change the gpc_order setting in your php3.ini file. The default setting is "GPC" which means that GET variables are parsed first followed by POST variables and lastly by COOKIE variables. This means that GET vars are overwritten by POST vars which are in turn overwritten by COOKIE vars. So, by default if you have the same variables in your GET and POST data the POST one will be the one that shows up in the main PHP symbol table and you would have to use the $HTTP_GET_VARS to get at it. Along with changing the order from "GPC" to something like "CGP" which would make POST variables have the highest priority, you can leave out any of the letters to completely disable PHP's ability to see a certain type of variable. If you never wanted GET-method data to be turned into PHP variables you could use a gpc_order setting of "PC".