std::ctype<char>::scan_is (3) - Linux Manuals
Defined in header <locale>
const char* scan_is (mask m, const char* beg, const char* end) const; (1)
Locates the first character in the character array [beg, end) that satisfies the classification mask m, that is, the first character c such that table()[(unsigned char) c] & m would return true.
If (unsigned char)c >= std::ctype<char>::table_size, then an implementation-defined value is substituted instead of table()[(unsigned char)c], possibly different for different values of c.
m - mask to search for
beg - pointer to the first character in an array of characters to search
end - one past the end pointer for the array of characters to search
Pointer to the first character in [beg, end) that satisfies the mask, or end if no such character was found.
Unlike the primary template std::ctype, this specialization does not perform a virtual function call when classifying characters. To customize the behavior, a derived class may provide a non-default classification table to the base class constructor.
// Run this code
do_scan_is locates the first character in a sequence that conforms to given classification
scan_not (public member function)