std::wcsxfrm(3)

NAME
std::wcsxfrm - std::wcsxfrm

Synopsis
   Defined in header <cwchar>
   std::size_t wcsxfrm( wchar_t* dest, const wchar_t* src, std::size_t count );
   Transforms the null-terminated wide string pointed to by src into the
   implementation-defined form such that comparing two transformed strings with
   std::wcscmp gives the same result as comparing the original strings with
   std::wcscoll, in the current C locale.
   The first count characters of the transformed string are written to destination,
   including the terminating null character, and the length of the full transformed
   string is returned, excluding the terminating null character.
   If count is 0, then dest is allowed to be a null pointer.

Notes
   The correct length of the buffer that can receive the entire transformed string is 1
   + std::wcsxfrm(nullptr, src, 0).
   This function is used when making multiple locale-dependent comparisons using the
   same wide string or set of wide strings, because it is more efficient to use
   std::wcsxfrm to transform all the strings just once, and subsequently compare the
   transformed wide strings with std::wcscmp.

Parameters
   dest - pointer to the first element of a wide null-terminated string to write the
           transformed string to
   src - pointer to the null-terminated wide character string to transform
   count - maximum number of characters to output

Return value
   The length of the transformed wide string, not including the terminating
   null-character.

Example
// Run this code
 #include <cwchar>
 #include <iostream>
 int main()
 {
     std::setlocale(LC_ALL, "sv_SE.utf8");
     std::wstring in1 = L"\u00e5r";
     std::wstring out1(1 + std::wcsxfrm(nullptr, in1.c_str(), 0), L' ');
     std::wstring in2 = L"\u00e4ngel";
     std::wstring out2(1 + std::wcsxfrm(nullptr, in2.c_str(), 0), L' ');
     std::wcsxfrm(&out1[0], in1.c_str(), out1.size());
     std::wcsxfrm(&out2[0], in2.c_str(), out2.size());
     std::wcout << "In the Swedish locale: ";
     if (out1 < out2)
         std::wcout << in1 << " before " << in2 << '\n';
     else
         std::wcout << in2 << " before " << in1 << '\n';
     std::wcout << "In lexicographical comparison: ";
     if (in1 < in2)
         std::wcout << in1 << " before " << in2 << '\n';
     else
         std::wcout << in2 << " before " << in1 << '\n';
 }

Output:
 In the Swedish locale: år before ängel
 In lexicographical comparison: ängel before år

See also
                transform a string so that strcmp would produce the same result as
   strxfrm strcoll
                (function)
   do_transform transforms a string so that collation can be replaced by comparison
   [virtual] (virtual protected member function of std::collate<CharT>)
   wcscoll compares two wide strings in accordance to the current locale
                (function)
   C documentation for
   wcsxfrm