How do I use strcasestr()?

Question

I #include <string.h> but when I call strcasestr(src, search); I get the following error message implicit declaration of function ‘strcasestr’. how to I compile: gcc-4.6 -Wall -lsqlite3 -lunac -Werror -O2 -o foo.out foo.c how to fix this? Thanks in advance.

Solution 1

As specified in the corresponding manpage, since strcasestr is a nonstandard extension you must #define _GNU_SOURCE before the #include <string.h> before any #include (other files may already include <string.h>, thanks @Cubbi for pointing out this potential problem); this can also easily be accomplished by specifying -D_GNU_SOURCE on the compiler command line.

Solution 2

You must add:

#define _GNU_SOURCE

before the string.h include, since the function is non-standard.

Comments

[Jack]

I added too the prototype function:#include <string.h> #define _GNU_SOURCE char *strcasestr(const char *haystack, const char *needle); and works fine now. Thanks very much.

[Matthew Flaschen]

@Jack, you do not need to (and should not) add the prototype. However, the define needs to be before the include.

[Cubbi]

Caveat: make sure that #define is the first line in the file. If you #include <stdio.h>, then #define _GNU_SOURCE, and then #include <string.h>, you won't get strcasestr because stdio.h already included string.h. The safe choice is compiling with -D_GNU_SOURCE.

[Hefaz]

I added that line as well, but still does not work. any help?

[Matteo Italia]

@Hefaz What compiler/platform are you using?

[Hefaz]

CodeBlocks in Windows. I solved the problem by defining that function. Thank you.