How to fix std::wcout printing question marks (?) on Linux

Problem:

You are trying to print a wstring from a wstring literal using std::wcout (with an UTF-8-encoded source file):

wstring w = L"Test: äöü";
wcout << w << endl;

but when you run this program, you see

Test: ???

Solution:

Use setlocale() to set a UTF-8 locale:

setlocale( LC_ALL, "en_US.utf8" );
wstring w = L"Test: äöü";
wcout << w << endl;

This will print

Test: äöü

as expected.

Full example

#include <string>
#include <iostream>

using namespace std;

int main() {
    setlocale( LC_ALL, "en_US.utf8" );
    wstring w = L"Test: äöü";
    wcout << w << endl;
}

Compile like this:

g++ -o main main.cpp