Defined in header <locale>
const char* scan_is (mask m, const char* beg, const char* end) const;

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

Return value

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.


#include <locale>
#include <iostream>
#include <iterator>
int main()
    std::locale loc("");
    auto& f = std::use_facet<std::ctype<char>>(loc);
    // skip until the first letter
    char s1[] = "      \t\t\n  Test";
    const char* p1 = f.scan_is(std::ctype_base::alpha, std::begin(s1), std::end(s1));
    std::cout << "'" << p1 << "'\n";
    // skip until the first letter
    char s2[] = "123456789abcd";
    const char* p2 = f.scan_is(std::ctype_base::alpha, std::begin(s2), std::end(s2));
    std::cout << "'" << p2 << "'\n";



See also

locates the first character in a sequence that conforms to given classification
(virtual protected member function of std::ctype<CharT>)
locates the first character in a sequence that fails given classification, using the classification table
(public member function)

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