Originální popis anglicky: 
strchr, strrchr - locate character in string
Návod, kniha: Linux Programmer's Manual
#include <string.h>
 
char *strchr(const char *s, int c);
 
char *strrchr(const char *s, int c);
The 
strchr() function returns a pointer to the first occurrence of the
  character 
c in the string 
s.
The 
strrchr() function returns a pointer to the last occurrence of the
  character 
c in the string 
s.
Here "character" means "byte" - these functions do not work
  with wide or multi-byte characters.
The 
strchr() and 
strrchr() functions return a pointer to the
  matched character or NULL if the character is not found.
SVID 3, POSIX, BSD 4.3, ISO 9899
index(3), 
memchr(3), 
rindex(3), 
strpbrk(3),
  
strsep(3), 
strspn(3), 
strstr(3), 
strtok(3),
  
wcschr(3), 
wcsrchr(3)