Program doesn't stop after returning 0 from main

Question

I wrote a program that encodes files with Huffman coding.
It works fine but for some reason after returning 0 from main function it doesn't stop.
Main function looks like:

int main(int argc, char *argv[])
{
    if (argc < 5)
    {
        std::cout << "..." << std::endl;
    }
    else
    {
        if (!std::strcmp(argv[1], "haff") && !std::strcmp(argv[2], "-c"))
            HuffmanC(argv[3], argv[4]);
        if (!std::strcmp(argv[1], "haff") && !std::strcmp(argv[2], "-d"))
            HuffmanD(argv[3], argv[4]);

        std::cout << "Operations: " << count << std::endl;
    }

    return 0;
}

When I run it, I get:

MacBook-Pro-Alex:code alex$ ./main haff -c test.txt test.haff
Operations: 37371553

It ends with an empty line and terminal says that the program keeps running, but the last cout statement executes well and as I get it it should return 0 and finish. How can I make it finish after returning 0? Or is the problem in the rest of the code?

If you have an empty main: `int main() {}`, does the program keep running as well? — Justin, Mar 23 '18 at 20:37
They'd have to spawn, and then orphan, other processes to have the behavior you're describing — Cory Kramer, Mar 23 '18 at 20:38
Run a stack trace by adding a breakpoint before it returns zero and see what processes remain. You have a major memory issue here. — Callat, Mar 23 '18 at 20:39
@NathanOliver even if they do, once main returns, all threads are terminated too. So this could not cause claimed behavior. — SergeyA, Mar 23 '18 at 20:42
I suggest running `pstack` (or MacOS version of it) on the process and see what is happening there. — SergeyA, Mar 23 '18 at 20:44

einpoklum · Accepted Answer · 2018-03-23T20:51:00.973

Or is the problem in the rest of the code?

Possibly. Perhaps you've corrupted your stack somehow, so that you're "returning" from main to someplace you didn't expect. We can't really know without an complete, verifiable example.

How can I make it finish after returning 0?

You can use the kill command on MacOS to terminate it forcefully. Using the GUI task manager may or may not work.

But perhaps a more effective course of action would be to attach a debugger to the process and see what it's actually doing.

You could read this explanation on how to do this on MacOS with XCode - but I don't use MacOS, so I wouldn't know. Also, @SergeyA graciously suggests trying using pstack to get the process' current stack. Of course, if the stack has been garbled, there's no telling what you'll actually get.

Make sure the application is compiled with debugging information included.

Finally - it's probably better to run the program with a debugger attached in the first place, and set a breakpoint at the last cout << line.

According to this (https://stackoverflow.com/questions/24523118/pstack-a-process-on-osx-10-9) one has to use lldb. — SergeyA, Mar 23 '18 at 20:49

Program doesn't stop after returning 0 from main

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