printf prints twice for some reason, cout seems okay though [closed]

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I've written a library and I'm trying to statically link it to my main program. My main program is written in C++, but the library is in C. I noticed some of the debugging printf statemen开发者_如何学Gots in my library running twice where they shouldn't for some reason, so I started commenting out code. I'm now left with this (comments excluded):

#include <iostream>
extern "C"
{
    include "audio.h"
}

int main(int argc, char** argv)
{
    std::cout << "Hello" << std::endl;
    audio_test();
    std::cout << "World" << std::endl;
    return 0;
}

The function audio test is not interesting at all. This is from a C file that I'm trying to use in my C++ project.

void audio_test()
{
    printf("TEST\n");
}

The output from my program is this:

Hello
TEST

TEST
World

I have no idea at this point why this is happening.

---

Call std::ios_base::sync_with_stdio(true) and it will probably work better.