Do you mean XS code? If so, perlapi:

newSVpv Creates a new SV and copies a string into it. The reference count for the SV is set to 1. If "len" is zero, Perl will compute the length using strlen(). For efficiency, consider using "newSVpvn" instead.
SV* newSVpv(const char *const s, const STRLEN len)

This creates a Perl scalar value from C string.