Go forward to strlwr
Go backward to strerror
Go up to Strings
Go to the top op libc

`strlen'--character string length

     #include <string.h>
     size_t strlen(const char *STR);
The `strlen' function works out the length of the string starting at
`*STR' by counting chararacters until it reaches a `NULL' character.
`strlen' returns the character count.
`strlen' is ANSI C.
   `strlen' requires no supporting OS subroutines.