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std:: wcsspn

From cppreference.net
C++
Text processing library
Null-terminated wide strings
Defined in header <cwchar>
size_t wcsspn ( const wchar_t * dest, const wchar_t * src ) ;

Returns the length of the maximum initial segment of the wide string pointed to by dest , that consists of only the characters found in wide string pointed to by src .

Contents

Parameters

dest - pointer to the null-terminated wide string to be analyzed
src - pointer to the null-terminated wide string that contains the characters to search for

Return value

The length of the maximum initial segment that contains only characters from wide string pointed to by src .

Example

Run this code 
#include <cwchar>
#include <iostream>
#include <locale>
int main()
{
    wchar_t dest[] = L"白猫 黑狗 甲虫";
    const wchar_t src[] = L" 狗猫 白黑 ";
    const std::size_t len = std::wcsspn(dest, src);
    dest[len] = L'\0'; // terminates the segment to print it out
    std::wcout.imbue(std::locale("en_US.utf8"));
    std::wcout << L"The length of maximum initial segment is " << len << L".\n";
    std::wcout << L"The segment is \"" << dest << L"\".\n";
}

Possible output: 

The length of maximum initial segment is 6.
The segment is "白猫 黑狗 ".

See also

returns the length of the maximum initial segment that consists
of only the wide not found in another wide string
(function)
finds the first location of any wide character in one wide string, in another wide string
(function)
C documentation for wcsspn