usage of strdup

Question

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

int main()
{    
    char *s;
    s = strdup("foo");
    printf("%s\n", s);
    getchar();
    return 0;
}

Looks pretty harmless, doesn't it ? But my IDE, which is Dev-C++, gives my the following warning: warning: assignment makes pointer from integer without a cast

The warning disappears if you would change the code like this:

char *s;
s = (char*)strdup("foo");

Can anyone help me explain this?

Answer 1

You're using Dev-C++, but strdup is not part of the C or C++ standard, it's a POSIX function. You need to define the proper (according to your IDE's documentation) preprocessor symbols in order for strdup to be declared by the header file ... this is necessary in order for the header file not to pollute the name space when included into conforming C or C++ source files.

For a simple portable alternative, consider

char* mystrdup(const char* s)
{
    char* p = malloc(strlen(s)+1);
    if (p) strcpy(p, s);
    return p;
}

Or, if you know strdup is actually in the library, you can copy its declaration from string.h into your own source file or header ... or use the simpler declaration from the man page:

char *strdup(const char *s);