strstr, strcasestr - locate a substring

       For an explanation of the terms used in this section, see attributes(7).
       ┌──────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │ Interface                                                            │ Attribute     │ Value          │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ strstr()                                                             │ Thread safety │ MT-Safe        │
       ├──────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │ strcasestr()                                                         │ Thread safety │ MT-Safe locale │
       └──────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

       The  strstr()  function  finds  the first occurrence of the substring needle in the string haystack.  The
       terminating null bytes ('\0') are not compared.

       The strcasestr() function is like strstr(), but ignores the case of both arguments.

strstr()
              POSIX.1-2001, C89.

       strcasestr()
              GNU.

       Standard C library (libc, -lc)

       strstr, strcasestr - locate a substring

       These functions return a pointer to the beginning of the located substring, or NULL if the  substring  is
       not found.

       If needle is the empty string, the return value is always haystack itself.

memchr(3),  memmem(3),  strcasecmp(3), strchr(3), string(3), strpbrk(3), strsep(3), strspn(3), strtok(3),
       wcsstr(3)

Linux man-pages 6.9.1                              2024-06-15                                          strstr(3)

strstr()
              C11, POSIX.1-2008.

       strcasestr()
              GNU.

#include<string.h>char*strstr(constchar*haystack,constchar*needle);#define_GNU_SOURCE         /* See feature_test_macros(7) */
       #include<string.h>char*strcasestr(constchar*haystack,constchar*needle);