Question

I have a problem when using printf and wprintf functions together in code. If the regular string is printed first, then wprintf doesn’t work. If I use wprintf first then printf doesn’t work.

#include <stdio.h>
#include <wchar.h>
#include <stdlib.h>
#include <locale.h>

int main() 
{
    setlocale(LC_ALL,"");

    printf("No printing!\n");
    wprintf(L"Printing!\n");
    wprintf(L"Wide char\n");
    printf("ASCII\n");
    return 0;
}

Outputs:

No printing!
ASCII

While

#include <stdio.h>
#include <wchar.h>
#include <stdlib.h>
#include <locale.h>

int main() 
{
    setlocale(LC_ALL,"");

    wprintf(L"Printing!\n");
    printf("No printing!\n");
    wprintf(L"Wide char\n");
    printf("ASCII\n");
    return 0;
}

outputs:

Printing!
Wide char

I’m using gcc (GCC) 4.6.1 20110819 together with glibc 2.14 on 64bit Linux 3.0.

Answer 1

This is to be expected; your code is invoking undefined behavior. Per the C standard, each FILE stream has associated with it an “orientation” (either “byte” or “wide) which is set by the first operation performed on it, and which can be inspected with the fwide function. Calling any function whose orientation conflicts with the orientation of the stream results in undefined behavior.