[Bug libstdc++/119880] New: fwide must be called before and after std::wcout to change wide orientation to allow std::cout works

[nickhuang99 at hotmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119880

            Bug ID: 119880
           Summary: fwide must be called before and after std::wcout to
                    change wide orientation to allow std::cout works
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nickhuang99 at hotmail dot com
  Target Milestone: ---

See following program which requires the first "fwide" so as to allow
"std::cout" to work after "std::wcout" calls. This behavior is only with GCC
library and MSVC latest can comment the first "fwide" out. This indicates a bug
in implementation of GCC stdlib.

#include <cwchar>
#include <iostream>
#include <ostream>
#include <cstdio>
int main() {    
    //std::fwide(stdout, -1); // you cannot comment out this line for GCC!!!
    std::wcout << L"This is a wide line from local wcout." << std::endl;   
    std::fwide(stdout, -1);
    std::cout << "This is a narrow line after wide output." << std::endl;  
    return 0;
}



In GCC family, only "std::wcout" prints while "std::cout" fails to print
because stdout is still wide oriented. This can be confirmed by a test
"fwide(stdout, 0) > 0" after "std::wcout" prints. 



See www.godbolt.org at https://www.godbolt.org/z/63Gh3xGMh