std::strxfrm(3)

NAME
std::strxfrm - std::strxfrm

Synopsis
   Defined in header <cstring>
   std::size_t strxfrm( char* dest, const char* src, std::size_t count );
   Transforms the null-terminated byte string pointed to by src into the
   implementation-defined form such that comparing two transformed strings with
   std::strcmp gives the same result as comparing the original strings with
   std::strcoll, 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.
   The behavior is undefined if the dest array is not large enough. The behavior is
   undefined if dest and src overlap.
   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::strxfrm(nullptr, src, 0).
   This function is used when making multiple locale-dependent comparisons using the
   same string or set of strings, because it is more efficient to use std::strxfrm to
   transform all the strings just once, and subsequently compare the transformed
   strings with std::strcmp.

Parameters
   dest - pointer to the first element of the array where the transformed string will
           be written
   src - pointer to the first character of a null-terminated byte string to transform
   count - maximum number of characters to be written

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

Example
// Run this code
 #include <cassert>
 #include <cstring>
 #include <iomanip>
 #include <iostream>
 #include <string>
 int main()
 {
     char* loc = std::setlocale(LC_COLLATE, "cs_CZ.iso88592");
     assert(loc);
     std::string in1 = "hrnec";
     std::string out1(1 + std::strxfrm(nullptr, in1.c_str(), 0), ' ');
     std::string in2 = "chrt";
     std::string out2(1 + std::strxfrm(nullptr, in2.c_str(), 0), ' ');
     std::strxfrm(&out1[0], in1.c_str(), out1.size());
     std::strxfrm(&out2[0], in2.c_str(), out2.size());
     std::cout << "In the Czech locale: ";
     if (out1 < out2)
         std::cout << in1 << " before " << in2 << '\n';
     else
         std::cout << in2 << " before " << in1 << '\n';
     std::cout << "In lexicographical comparison: ";
     if (in1 < in2)
         std::cout << in1 << " before " << in2 << '\n';
     else
         std::cout << in2 << " before " << in1 << '\n';
 }

Possible output:
 In the Czech locale: hrnec before chrt
 In lexicographical comparison: chrt before hrnec

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