strstr() - locate a substring in a string
#include <string.h>
char * strstr (const char *big, const char *little)
The strstr(3) function locates the first occurrence of the null-terminated string little in the null-terminated string big. If little is the empty string, strstr(3) returns big; if little occurs nowhere in big, strstr(3) returns NULL; otherwise strstr(3) returns a pointer to the first character of the first occurrence of little.
memchr(3)
strchr(3)
strcspn(3)
strpbrk(3)
strrchr(3)
strsep(3)
strspn(3)
strtok(3)