How to assign a returned char pointer to an array

Your code has the following problems:

1. You should provide a prototype declaration of the function parseString before using it in main.

2. If you want the function parseString to return a pointer to a string, then you should make the return type of the function char * instead of void const char*.

3. If you declare the parameters of the function parseString to be of type char*, then you are not allowed to pass that function an argument of type const char *. However, since the function parseString does not modify the strings pointed to by its arguments, you can declare the parameters to be const char * instead of char *, which will solve your problem.

After fixing these issues, your could will look like this:

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

char* parseString( const char* str, const char* first, const char* snd);

int main(int argc, char *argv[])
{
    const char *s = "[[random text]]";

    const char *P1 = "[[";
    const char *P2 = "]]";
    const char *result = parseString(s,P1,P2);
    printf("%s",result);
} 

char* parseString( const char* str, const char* first, const char* snd)
{
    char *target = NULL;
    char *start, *end;

    if ( start = strstr( str, first ) )
    {
        start += strlen( first );
        if ( end = strstr( start, snd ) )
        {
            target = ( char * )malloc( end - start + 1 );
            memcpy( target, start, end - start );
            target[end - start] = '\0';
        }
    }
    return target;
}