The c-strstr module contains a substring search function operating
on single-byte character strings, that operate as if the locale encoding
was ASCII.
(The "C" locale on many systems has the locale encoding "ASCII".)
The function is:
extern char *c_strstr (const char *haystack, const char *needle);
Note: The function strstr from <string.h> supports only
unibyte locales;
for multibyte locales, you need the function mbsstr.