C Header file error: expected identifier or ‘(’ before ‘[’ token

I'm a complete c newb. I'm trying to define a few functions in a header file and then implement them in a separate file. But when I try running gcc runtime.c I get the following error:

In file included from runtime.c:1:
runtime.h:7: error: expected identifier or ‘(’ before ‘[’ token

Here's the contents of runtime.h:

#ifndef HEADER
#define HEADER

/*given two arrays of ints, add them

 */
int[] * _addInts(int[] *x, int[] *y);

#endif

What's the er开发者_如何学Pythonror? I tried browsing header files but they started adding things like "extern" and "intern" and crazy ifdef's. Thanks for your help, Kevin

---

You should just pass pointers (since if you pass arrays to a function, what;'s really passed is a pointer anyway). Also, you can't return an array - again, just return a pointer:

int* _addInts(int *x, int *y);  // equivalent to: int* _addInts(int x[], int y[]);

You'll also have to arrange for the number of elements to be passed in somehow. Something like the following might work for you:

int* _addInts(int *x, int *y, size_t count);

Also - do not fall into the trap of trying to use sizeof on array parameters, since they're really pointers in C:

int* _addInts(int x[], int y[])
{
     // the following will always print the size of a pointer (probably
     //     4 or 8):
     printf( "sizeof x: %u, sizeof y: %u\n", sizeof(x), sizeof(y));
}

That's one reason why I'd prefer having the parameters be declared as pointers rather than arrays - because they really will be pointers.

See Is there a standard function in C that would return the length of an array? for a macro that will return the number of elements in an array for actual arrays and will cause a compiler error (on most compilers) much of the time when you try to use it on pointers.

If your compiler is GCC, you can use Linux's trick: Equivalents to MSVC's _countof in other compilers?

---

Get rid of each "[]"

As an array is a pointer, you only need to pass the pointers, like so:

int* _addInts(int* x, int* y);

EDIT: Also pass the size.

---

Use:

int* addInts(int* x, int* y, int size);

---

You have the [] in the wrong locations. The syntax for declaring arrays in "C" has the [] coming after the item you want to be an array, not between the type declaration and the item (like Java and C# use). I am not sure what you are trying to declare, but here are some options:

If you are trying to declare that you will be using a function named "_addInts()" that returns a pointer to an int, and takes as its parameters two separate arrays of pointers to integers named x and y --

int * _addInts(int *x[], int *y[]);

If you want to declare a function that returns an array of integer pointers:

int * _addInts(int *x[], int *y[])[];

If _addInts is a function that takes two arrays of int (as opposed to arrays of int *):

int * _addInts(int x[], int y[]);

Note that the following are (nearly) equivalent, and can be used interchangeably in declarations such as you are attempting.

int *x

and

int x[]

as are:

int **x

and

int *x[]