CODEWITHSUNDEEP
c++crashcoutostreamatexit
Tri-Edge AI
Tri-Edge AI

Reputation: 340

Strange crash with C++ atexit() function

I am using MSVC with Visual Studio 2013. This is the code I am compiling:

#include <iostream>
using namespace std;

void crash()
{
    cout << "crash?" << endl;
    system("PAUSE");
}

int main(int argc, char *argv[])
{
    atexit(crash);
    //while(true);
    return 0;
}

The way it is right now - it works like a charm. I start the program, it goes inside the crash function, pauses, I press a key and it closes normally. All cool. However, if I uncomment the while loop and use the X button on the console to close it, I get a crash inside the endl function. I was able to determine that the crash is caused by _Ostr.widen() This is the implementation of the endl function, provided by MSVC:

template<class _Elem,
    class _Traits> inline
    basic_ostream<_Elem, _Traits>&
        __CLRCALL_OR_CDECL endl(basic_ostream<_Elem, _Traits>& _Ostr)
    {   // insert newline and flush stream
    _Ostr.put(_Ostr.widen('\n'));
    _Ostr.flush();
    return (_Ostr);
    }

Using Ctrl+C to terminate the program causes the same effect. How can I fix this?

Upvotes: 1

Views: 1284

Answers (1)

Tri-Edge AI
Tri-Edge AI

Reputation: 340

Seems like my suspicions turned out to be true. I modified the code like so:

#include <iostream>
using namespace std;

#include <Windows.h>

void crash()
{
    printf("%i\n", GetCurrentThreadId());
    system("PAUSE");
}

int main()
{
    printf("%i\n", GetCurrentThreadId());

    atexit(crash);
    //while(true);

    return 0;
}

When the program exists normally both printf()s display identical thread IDs, however when I press Ctrl+C or the X button the thread IDs are different, which explains the crash and makes a lot of sense when you think about it. Thus, here is a small example how this issue can be tackled:

#include <iostream>
#include <conio.h>
using namespace std;

#include <Windows.h>

volatile bool wantClose = false;

void OnExit()
{
    cout << GetCurrentThreadId() << endl;
    system("PAUSE");
}

BOOL WINAPI OnConsoleClose(DWORD dwCtrlType)
{
    wantClose = true; // set a flag that the console wants us to close
    ExitThread(0); // kill this thread immediately so it doesn't make the console stuck
    return FALSE;
}

int main()
{
    cout << GetCurrentThreadId() << endl;

    SetConsoleCtrlHandler(OnConsoleClose, TRUE); // handle close requests from the console
    atexit(OnExit);
    while(!wantClose); // at some point in our code we will have to check whether the console wants us to close down

    return 0;
}

Please note: The usage of system("PAUSE") and busy waiting are only for the sake of keeping the example simple. I do not advise their usage in real code.

Upvotes: 1

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