Code blocks MinGW and the %n conversion character

Question

I am trying to use a conversion character to count the number of chars printed so far with the following code.

#include <stdio.h>
int main(void) {
    int n;
    printf("%s: %nFoo\n", "hello", &n);
    printf("%*sBar\n", n, "");
}

When working correctly this code prints Hello Foo, then on the next line Bar is aligned with Foo.

This works fine when compiled with GCC on my linux box. However, when compiled using minGW in code blocks on my Windows PC %n does not work, and all that is printed is hello: Bar all on one line. Why so and can I fix this?

Answer 1

use compile option -D__USE_MINGW_ANSI_STDIO

E.g

>gcc prog.c -D__USE_MINGW_ANSI_STDIO

or

>clang prog.c -D__USE_MINGW_ANSI_STDIO

---

Another solution is placing this command above the first import statement like so (see below). This will ensure that the ANSI I/O standards are preferred over Microsoft's. More information in this link here.

#define __USE_MINGW_ANSI_STDIO 1
#include <stdio.h>

Answer 2

It looks like this is a Windows issue, this article says:

The default C-RunTime Library (msvcrt.dll) on Vista seems to have %n disabled by default - security reasons of course

It looks like there is a _set_printf_count_output to enable it.

BLUEPIXY found that in order to get it working outside Visual Studio you need to define __USE_MINGW_ANSI_STDIO:

#define __USE_MINGW_ANSI_STDIO 1