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I am able to compile the following using gcc version 4.7.2

   #include <string.h>

   int main(){
    char text[] = "String duplicate";
    char* dup = strdup(text);
    return 0;

   }

But when I used the --std=c11 flag, I get the following warning:

warning: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration]
warning: initialization makes pointer from integer without a cast [enabled by default]

What changed to cause this warning?

Mike Fisher
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  • Related : [How do I remove the following 'implicit declaration of function' warnings?](http://stackoverflow.com/q/9427145/1870232) – P0W Oct 28 '13 at 17:43
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    [This mail](http://lists.opensuse.org/opensuse-factory/2012-06/msg00102.html) suggests `strdup` is standard in C11, but I can't find it anywhere else. – Kninnug Oct 28 '13 at 17:46
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    I don´t think strdup is a C standard, as far I remember is only a POISX function. – Jonatan Goebel Oct 28 '13 at 17:46

2 Answers2

9

Read the manual of strdup by

man strdup

You can find that

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

strdup(): _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

It denotes that strdup conforms to SVr4, 4.3BSD, POSIX.1-2001.

So you can get rid of the warnings by

gcc -D_BSD_SOURCE -std=c11 <your source file>

I guess the warnings are caused by c11 not enabling one of the above macros.

Like
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6

you want --std=gnu11 or --std=c11 -D_GNU_SOURCE

JTAS
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