namespace confusion...

[squarehead]

I am trying to be very careful about using namespaces, but it seems like my compiler is aware of names even though I have not provided a namespace. How does this happen? Today I successfully managed to write a program that prints the current time to the console. I am frustrated to see that it compiles without any issues. :) It's a good problem to have I know, but I need to understand.

#include <iostream>
#include <chrono>
//#include <ctime>

int main()
{
    std::chrono::system_clock::time_point hammerTime = std::chrono::system_clock::now();
    time_t tt = std::chrono::system_clock::to_time_t(hammerTime);
    struct tm *timeInfo = localtime(&tt);
    std::cout << timeInfo->tm_hour << ":"
              << timeInfo->tm_min << ":"
              << timeInfo->tm_sec << std::endl;
    return 0;
}

As far as I know 'time_t', 'tm', and 'localtime' are all defined in the ctime header, which I have not included. I also did not prefix those names with a namespace. So how does the compiler recognise them? They are surely not registered keywords of C++.

[JLBorges]

See: http://www.cplusplus.com/forum/general/99615/
And: http://www.cplusplus.com/forum/beginner/127932/

[keskiverto]

MSVC 12.0 has <chrono>. It starts:

// chrono C++11 header
#pragma once
#ifndef _CHRONO_
#define _CHRONO_
#ifndef RC_INVOKED
#include <limits>
#include <ratio>
#include <utility>
#include <time.h> 

There you see the C-style header that adds stuff to the global namespace.

In other words library headers may include other library headers. Some implementations do so more than others.

[squarehead]

It partially circumvents the whole idea with namespaces. But I guess it's one of those things I just have to accept. Names from the original C library all over the place. *sigh* What a mess.

Anyway, thank you both for clearing this up.