CODEWITHSUNDEEP
c++terminalprogram-entry-point
Caladin00
Caladin00

Reputation: 356

Rerunning my main method

I just finished an image editor that is run through terminal console commands. After an image is edited, I'm trying to get the entire program (via a main() method) to run again but I'm a bit confused on how to do so. Here's the method I tried using to rerun the code.

void rerun()
{
    cout << "Would you like to alter another image? (Y/N) ";
    string answer;
    getline(cin, answer);
    while (answer != "Y" || answer != "N")

        if (answer == "N") {
            return;
        }
    if (answer == "Y") {
        main();
    }
}

This isn't giving me anything. What do I need to fix?

Upvotes: 3

Views: 796

Answers (1)

Sam Varshavchik
Sam Varshavchik

Reputation: 118425

The C++ standard prohibits the direct invocation of main(), like you're attempting to do:

3.6 Start and termination

...

3 - The function main shall not be used within a program.

main() can only be invoked from your environment, by your operating system. You cannot invoke it directly.

Therefore, you need to restructure the logic of your program, so that it has the effect of rerunning your entire program, when needed. For example:

int main(int argc, char **argv)
{
    int ret;

    do
    {
        ret = your_real_main(argc, argv);
    } while (ret == -1);

    return ret;
}

Whatever you have in your current main(), rename it as you_real_main() (and declare it accordingly), and if your_real_main() returns -1, it will be reexecuted, as if it was invoked again. All other return values get returned from main() itself, and carry whatever implication they do, for your C++ implementation.

Feel free to use any special return value from your_real_main(), instead of -1, for this behavior.

Of course, you are responsible for doing whatever is necessary to make this work correctly. Such as cleaning up all the resources you allocated, so by the time your_real_main() returns, everything that's been allocated has been freed, and the state of your application is identical to what it was when it was started (all dynamically-allocated memory has been released, all files have been closed, etc...).

With some careful planning, it is also possible to implement the same result by using a carefully-thrown exception, rather than a special return value. Then there may be operating system-specific means of accomplishing the same goals, such as exec() on Linux, also...

Upvotes: 2

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