The strstr of C language (function) learning Strcasestr

First, the STRSTR function uses

[1] function prototypes

Char *strstr (const char *haystack, const char *needle);

[2] header file

#include <string.h>

[3] function function

Search for the first occurrence of "substring" in "specified string"

[4] parameter description

Haystack        --the target string that is being looked for "parent string" needle          --The string object "substring" to find

Note: If needle is null, the " parent string " is returned

[5] return value

(1) Successfully found, returns the char * pointer (2) where the first occurrence in the parent string is not found, that is, there is no such substring, returns: "NULL"

[6] examples of programs

#include <stdio.h> #include <string.h>int main (int argc, char *argv[]) {    char *res = strstr ("Xxxhost: Www.baidu.com "," host ");    if (res = = NULL) printf ("Res1 is null!\n");    else printf ("%s\n", res);    Print:--> ' host:www.baidu.com '    res = strstr ("xxxhost:www.baidu.com", "Cookie");    if (res = = NULL) printf ("Res2 is null!\n");    else printf ("%s\n", res);    Print:--> ' Res2 is null! '    return 0;}

[7] special Instructions

Note: The parameters in the STRSTR function are strictly " case-sensitive "

Second, strcasestr function

[1] description

The function and use method of STRCASESTR function is basically consistent with strstr.

[2] differences

The STRCASESTR function is "case insensitive" when comparing "substring" to "parent string"

[3] function prototypes

#define _GNU_SOURCE#INCLUDE <string.h>char *strcasestr (const char *haystack, const char *needle);

[4] examples of programs

#define _GNU_SOURCE             //macro definition must have, otherwise the compilation will have warning warning message # include <stdio.h> #include <string.h>int main (int ARGC, Char *argv[]) {    char *res = strstr ("xxxhost:www.baidu.com", "Host");    if (res = = NULL) printf ("Res1 is null!\n");    else printf ("%s\n", res);     Print:--> ' host:www.baidu.com '    return 0;

[5] Important details

If you do not define a "_gnu_source" macro when programming, there will be a warning message when compiling

Warning:initialization makes pointer from integer without a cast

Reason:

The STRCASESTR function is not a standard C library function, it is an extension function. The function returns the int type without declaring the default before the call

Solve:

To add #define _gnu_source before all header files include  

Another workaround: (but not recommended)

Under Define header file, manually add the prototype declaration of the STRCASESTR function yourself

#include <stdio.h>, .... extern char *strcasestr (const char *, const char *);         This method can also eliminate compile-time warning messages

The strstr of C language (function) learning Strcasestr