std::strxfrm

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

Return value

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

Example

#include <iostream>
#include <iomanip>
#include <cstring>
#include <string>
#include <cassert>
 
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';
 
}

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

See also