What is exact meaning of iostream is sync with ios_base::sync_with_stdio

Question

Is this simply means whatever we do with object like cout gets in sync with stdout (and vice versa?). What does this exactly mean. Is stdio also sync with stdout?

Answer 1

If the synchronization is off, the C++ streams will be faster in some cases.

By default, all standard C++ streams are synchronized with their respective C streams.

Example:

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    cout.sync_with_stdio(false);
    cout << "Hello\n";
    printf("World\n");
    cout << "...\n";
}

Output:

Hello
...
World

Changing it to true gives default result in order. Output:

Hello
World
...

Answer 2

The default ostream used by std::cout and stdio(like printf) is stdout, but it is not necessarily so.

The output could alway be redirected to the other destination. Referencing this: http://www.tldp.org/LDP/abs/html/io-redirection.html