They are non-standard functions from Microsoft’s C library. MS has since deprecated them in favor of renamed functions _strlwr()
and _strupr()
:
Note that the MS docs claim they are POSIX functions, but as far as I can tell they never have been.
If you need to use them on a non-MS toolchain, they’re easy enough to implement.
char* strlwr(char* s)
{
char* tmp = s;
for (;*tmp;++tmp) {
*tmp = tolower((unsigned char) *tmp);
}
return s;
}