std:: wmemchr

From cppreference.com
C++
Strings library
Null-terminated wide strings
Defined in header <cwchar>
const wchar_t * wmemchr ( const wchar_t * ptr, wchar_t ch, std:: size_t count ) ;
(1)
wchar_t * wmemchr ( wchar_t * ptr, wchar_t ch, std:: size_t count ) ;
(2)

Locates the first occurrence of wide character ch in the initial count wide characters of the wide character array pointed to by ptr .

If count is zero, the function returns a null pointer.

Parameters

ptr - pointer to the wide character array to be examined
ch - wide character to search for
count - number of wide characters to examine

Return value

Pointer to the location of the wide character, or a null pointer if no such character is found.

Example

Run this code 
#include <clocale>
#include <cwchar>
#include <iostream>
#include <locale>
 
int main()
{
    const wchar_t str[] = L"诺不轻信，故人不负我\0诺不轻许，故我不负人。";
    wchar_t target = L'许';
    const std::size_t sz = sizeof str / sizeof *str;
    if (const wchar_t* result = std::wmemchr(str, target, sz))
    {
        std::setlocale(LC_ALL, "en_US.utf8");
        std::wcout.imbue(std::locale("en_US.utf8"));
        std::wcout << "Found '" << target << "' at position " << result - str << '\n';
    }
}

Possible output: 

Found '许' at position 14

See also

searches an array for the first occurrence of a character
(function)
finds the first occurrence of a character
(function)
finds the first occurrence of a wide character in a wide string
(function)
(C++11)
finds the first element satisfying specific criteria
(function template)
C documentation for wmemchr
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