Setvbuf() problem when speeding console

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C++

In order to spped the console output in windows it is recommended to use setvbuf().
My problem is that after making the buffer, cout does not work in called functions.

I had to insert at the following program at main() the line:

cout<<"=== FIN ==="<<endl;

So:
1. How force to write at cout within the function?
2. What happens if writting size is bigger than the buffer size?

What I have tried:

<pre>#include <iostream>
using namespace std;
void test1(){cout<<" function ini"<<endl;} //" function ini" is not written here

int main()
{
#ifndef __linux__   //Introduce this code at the beginning of main() to increase a lot the speed of cout in windows: 
	char buffer_setvbuf[1024];setvbuf(stdout, buffer_setvbuf, _IOFBF, sizeof buffer_setvbuf); 
#endif

	cout<<"=== INI ==="<<endl;
	test1();
	cout<<"=== FIN ==="<<endl;
}

Note: I tried also set buffer_setvbuf[] as a global variable with same results.