Question

I have trouble understanding c header files and source files. I have:

something.c

#include <stdio.h>
#include "something.h"

typedef struct {
    int row, col;
} point;

point
whereispoint(point **matrix, int rows, int cols)
{
   ..... Does something ....
   printf("something...");
}

something.h

typedef struct point * p;

p whereispoint(p **matrix, int rows, int cols);

main.c

#include <stdio.h>
#include "something.h"

int
main(void)
{
   int row, col;
   p **matrix=malloc(bla, bla);
   .....Something.....
   p=whereispoint(matrix, row, col);
   return 0;
}

Now when I don’t actually know how to compile this… I tried gcc -c main.c something.c
but that doesn’t work, I tried to compile separately gcc -c main.c and gcc -c something.c
then main.c works but something.c does not.

I am actually trying to make a library out of something.c but as I am not able even to compile it to object code I don’t know what to do. I guess there is something wrong with the struct type and the typedef of it in something.h but I can’t figure out what…

Answer 1

In the header, the function whereispoint() is declare as returning a struct point* (the typedef p) but the definition returns a struct point, not a pointer.

Personally, I find typedef pointers confusing and think it is clearer in the code if * is used to denote a pointer:

/* header */
typedef struct point point_t;

point_t* whereispoint(point_t** matrix, int rows, int cols);

/* .c */
struct point {
    int row, col;
};

point_t* whereispoint(point_t** matrix, int rows, int cols)
{
   ..... Does something ....
   printf("something...");
   return ??;
}