This C++ program cannot be terminated by ctrl + C. Why?

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I was working on a C++ code, which for some unknown reason, does not terminate by Ctrl + C.

The below code is a reduced version of the code I was working on and it has the same issue. Moreover, if I don't take an input for M (remove '>>M') or remove vector a(n) or initialize the size of vector a by an integer literal instead or compile the code without -O3 compiler flag, the program terminates by Ctrl + C as expected.

Operating System: Windows 10
Compiler: MinGW
Compilation command: g++ -O3 -std=c++14

C++

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int N,M;
    cin>>N>>M;
    vector a(N);
}

What I have tried:

I have no idea why this behaviour is happening and cannot find any resource to explain the same.

Posted 5-Nov-19 0:55am

Shubham Avasthi

Updated 5-Nov-19 21:10pm

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Stefan_Lang · Answer 1 · 2019-11-05T21:11:00

I strongly suspect this is a bug in the compiler's code optimization: M isn't read by the program, so the compiler will try to eliminate code referring to it - maybe it messed up this optimization because the statement cin>>N>>M internally translates into a nested function call: operator>>(operator>>(cin, N), M). Optimizing M away out of that nested call could be tricky for the compiler with regard to how the state of cin is affected. - maybe it's left in a strate where it eats all input, including ^C ...

Disabling optimization, forcing a read on M later in the program, or splitting the input line in two all could help avoiding this error, but since I don't have MinGW I can't test that.

While of course you can never be sure to avoid a compiler error that you don't know about, I've found that, if a program doesn't do what it's supposed to, it's best to simplify the code statements and see if that helps.

CPallini · Answer 2 · 2019-11-05T01:11:00

Solution 1

On my Linux box (Ubuntu 18), the following program

C++

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    int N,M;
    cin>>N>>M;
    vector<int> a(N);
}

compiled with the g++ -O3 -std=c++14 (g++ 7.4.0) behaves as espected.

Posted 5-Nov-19 1:11am

CPallini

Comments

Stefan_Lang 5-Nov-19 10:53am

Same for vc14.0 on W10. Sounds like a compiler code optimization issue to me.

RickZeeland · Answer 3 · 2019-11-05T01:15:00

Solution 2

Might be a debugger issue, see: Workaround for GDB Ctrl-C Interrupt | MinGW[^]

Posted 5-Nov-19 1:15am

RickZeeland