C Interview Questions - Part 7

1.1 How should I decide which integer type to use?

1.2 Why aren't the sizes of the standard types precisely defined?

1.3 Since C doesn't define sizes exactly, I've been using typedefs like int16 and int32. I can then define these typedefs to be int, short, long, etc. depending on what machine I'm using. That should solve everything, right?

1.4 What should the 64-bit type be on a machine that can support it?

1.5 What's wrong with this declaration?

char* p1, p2;

I get errors when I try to use p2.

1.6 I'm trying to declare a pointer and allocate some space for it, but it's not working. What's wrong with this code?

char *p;
*p = malloc(10);

1.7 What's the best way to declare and define global variables and functions?

1.8 How can I implement opaque (abstract) data types in C?

1.9 How can I make a sort of ``semi-global'' variable, that is, one that's private to a few functions spread across a few source files?

1.10 Do all declarations for the same static function or variable have to include the storage class static?

1.11 What does extern mean in a function declaration?

1.12 What's the auto keyword good for?

1.13 What's the difference between using a typedef or a #define for a user-defined type?

1.14 I can't seem to define a linked list successfully. I tried

typedef struct {
char *item;
NODEPTR next;
} *NODEPTR;

but the compiler gave me error messages. Can't a structure in C contain a pointer to itself?

1.15 How can I define a pair of mutually referential structures? I tried

typedef struct {
int afield;
BPTR bpointer;
} *APTR;

typedef struct {
int bfield;
APTR apointer;
} *BPTR;

but the compiler doesn't know about BPTR when it is used in the first structure declaration.

1.16 What's the difference between these two declarations?

struct x1 { ... };
typedef struct { ... } x2;

1.17 What does

typedef int (*funcptr)();

mean?

1.18 I've got the declarations

typedef char *charp;
const charp p;

Why is p turning out const, instead of the characters pointed to?

1.19 I don't understand why I can't use const values in initializers and array dimensions, as in

const int n = 5;
int a[n];

1.20 What's the difference between const char *p, char const *p, and char * const p?

1.20b

What does it mean for a function parameter to be const? What do the two const's in

int f(const * const p)

mean?

1.21 How do I construct declarations of complicated types such as ``array of N pointers to functions returning pointers to functions returning pointers to char'', or figure out what similarly complicated declarations mean?

1.22 How can I declare a function that can return a pointer to a function of the same type? I'm building a state machine with one function for each state, each of which returns a pointer to the function for the next state. But I can't find a way to declare the functions--I seem to need a function returning a pointer to a function returning a pointer to a function returning a pointer to a function..., ad infinitum.

1.23 Can I declare a local array (or parameter array) of a size matching a passed-in array, or set by another parameter?

1.24 I have an extern array which is defined in one file, and used in another:

file1.c: file2.c:

int array[] = {1, 2, 3}; extern int array[];

Why doesn't sizeof work on array in file2.c?

1.25 My compiler is complaining about an invalid redeclaration of a function, but I only define it once and call it once.

1.25b What's the right declaration for main?
Is void main() correct?

1.26 My compiler is complaining about mismatched function prototypes which look fine to me.

1.27 I'm getting strange syntax errors on the very first declaration in a file, but it looks fine.

1.28 My compiler isn't letting me declare a big array like

double array[256][256];

1.29 How can I determine which identifiers are safe for me to use and which are reserved?

1.30 What am I allowed to assume about the initial values of variables and arrays which are not explicitly initialized?
If global variables start out as ``zero'', is that good enough for null pointers and floating-point zeroes?

1.31 This code, straight out of a book, isn't compiling:

int f()
{
char a[] = "Hello, world!";
}

1.31b What's wrong with this initialization?

char *p = malloc(10);

My compiler is complaining about an ``invalid initializer'', or something.

1.32 What is the difference between these initializations?

char a[] = "string literal";
char *p = "string literal";

My program crashes if I try to assign a new value to p[i].

1.33 Is char a[3] = "abc"; legal?

1.34 I finally figured out the syntax for declaring pointers to functions, but now how do I initialize one?

1.35 Can I initialize unions?