CODEWITHSUNDEEP
c++gccmingw
Makaveli84
Makaveli84

Reputation: 494

Run-time error in program compiled with MinGW gcc/g++ (nuwen distro)

#include <iostream>
#include <random>

using namespace std;

class myclass
{
    private:

    static bool randomBit()
    {
        std::random_device rd; // Obtain a random seed number from hardware
        std::mt19937 gen(rd()); // Initialize and seed the generator <---- CRASH!!
        uniform_int_distribution<> distr(0, 1); // Define the distribution range

        return distr(gen);
    }

    myclass::myclass() = delete; // Disallow creating an instance of this object

    public:

    static bool generateRandomBit()
    {   
        return randomBit();
    }
};

int main()
{   
    cout<<myclass::generateRandomBit()<<endl;

    return 0;
}

This compiles and runs without problems with MSVC. It compiles without errors with gcc but the mt19937 gen(rd()); line causes the program to crash with the following message:

"myprog.exe has stopped working

A problem caused the program to stop working correctly. Windows will close the program and notify you if a solution is available."

Any ideas?

gcc command: g++ mycode.cpp -fpermissive -s -o myprog.exe

UPDATE: Adding -O2 to the compiling command gets the program to run, albeit incorrectly so. The "random" function is no longer random; it always returns 1. For example, testing with the following "main" code...

int main()
{   
    int a[2] {0, 0};

    for (int i = 0; i < 1000; i++) {
        a[myclass::generateRandomBit()]++;
    }

    cout<<"<"<<a[0]<<", "<<a[1]<<">"<<endl;

    return 0;
}

...yields this output: <0, 1000>

Upvotes: 0

Views: 740

Answers (1)

Kaznov
Kaznov

Reputation: 1163

It appears that this is a problem with nuwen distro. Both 16.0 and 16.1 versions generate some kind of Undefined Behavior on std::random_device constructor or during value generation, what sometimes results in silent crash, but it is hard to create a minimalistic example.

Crashes seem to disappear, when code is compiled with optimization level greater than 0. I wouldn't depend on it, as most likely UB still exists there somewhere, and program can crash in the most unexpected places.

Version 16.0 uses GCC 8.1.0 and 16.1 uses GCC 8.2.0. I couldn't reproduce this bug with MinGW downloaded from https://sourceforge.net/projects/mingw-w64/, that uses 8.1.0 version too.

Also, mind that std::random_device on MinGW won't provide random numbers - it will be deterministic, always giving the same values. Unfortunately standard allows it, what is in my opinion a big issue.

If you just need different values with each run, consider seeding with other, not-random sources, like time from C library. If you really need non-deterministic values, you can use boost::random::random_device (same interface as std::random_device), provided with nuwen distro. It is not header-only though, so you need to add extra linking:

g++ foo.cpp -lboost_random -lboost_system

Upvotes: 1

Related Questions