如何正确定义函数返回的结构？

Question

I am trying to create a function which allocates memory for a structure array defined in "main". The problem seems to be that my function does not recognize the structure. What is wrong with the following code?

#include <math.h>
#include <stdio.h>
#include <stdlib.h>   

typedef struct typecomplex { float r; float i;  } complex;
complex *myfunction(int n);

int main (int argc, char *argv[]) {
    complex *result = myfunction(1000);
    exit(0);
}

... and in another file...

struct complex *myfunction(int n)  {
  complex *result = (complex *)malloc(n*sizeof(*complex));
  if(result==NULL) return(NULL);
      else return(result);
}

Answer 1

Building on fvdalcin's answer:

myprog.c:

#include <math.h>
#include <stdio.h>
#include <stdlib.h>   
#include "mycomplex.h"


int main (int argc, char *argv[]) {
    complex *result = myfunction(1000);
    exit(0);
}

mycomplex.h:

#ifndef __MYCOMPLEX_H__
typedef struct typecomplex { float r; float i;  } complex;
complex *myfunction(int n);
#define __MYCOMPLEX_H__
#endif

(The #ifdef's are a good idea to keep it from being included more than once.)

mycomplex.c:

#include <stdlib.h>
#include "mycomplex.h"

complex *myfunction(int n)  {
  complex *result = malloc(n*sizeof(complex));
  if(result==NULL) return(NULL);
      else return(result);
}

Note subtle but important fixes here--sizeof(complex) instead of sizeof(complex*), declaration of myfunction() doesn't include the keyword "struct", and no cast on malloc()--it doesn't need one and can hide the fact that you may be missing the include file with its prototype (see Do I cast the result of malloc? ). myfunction() could actually by simplified down to one line:

return malloc(n*sizeof(complex));

Answer 2

Move this declaration typedef struct _complex { float r; float i; } complex; typedef struct _complex { float r; float i; } complex; to the "other" file. This other file has to be your foo.h file, which has an foo.c equivalent which implements the methods declared in the foo.h . Then you can simply add the foo.h to your main.c file and everything will work fine.

Answer 3

Here is a code with corrections that compiles well:

typedef struct typecomplex { float r; float i;  } complex;
complex *myfunction(int n)  {          
  complex *result = (complex *)malloc(n*sizeof(complex)); //removed * from sizeof(*complex)
  if(result==NULL) return(NULL);
      else return(result);
}

int main (int argc, char *argv[]) {
    complex *result = myfunction(1000);
    exit(0);
}