Why is C++ getline() non-blocking when program is called from python subprocess?

I have a C++ program that waits for some text input with getline(), and it works well from the command line.

However, I would like to call it from Python – send some text, get the output, and have it wait for more input.

I tried with subprocess, but it seems that getline() in this case doesn’t wait for input but gets an empty line. It works as intended if I constantly send input, but as soon as I stop doing that, it starts reading empty strings.

Adding if (!input_command.empy()) in C++ works, but in this way the program consumes a lot of resources (I suppose because it keeps cycling the loop).

Is it possible to have getline() stop and wait for some actual input?

C++:

bool ExitProg = FALSE;
do{
    string input_command;
    getline(cin, input_command)
       
    if (input_command == std::string("something")){
        cout << "something" << endl;
    }
    
    if (input_command == std::string("exit")){
        ExitProg = True;
    }
    
} while (!ExitProg)

Python:

process = subprocess.Popen('c_program.exe', stdin=subproces.PIPE, stdout=subprocess.PIPE)
process.stdin.write('somethingn')
process.stdin.flush()
print(process.stdout.readline())

UPDATE: I assumed that the program was reading empty lines for the following reason. In the C++ program, I split the input line into an array and, when the python code was finished, I was getting an error from the C++ program about an element of the array not existing.

Answer

I created a class and added the start of the subprocess to the __init__ method. The methods of the class are used to interact with the C++ program. At this point however I was still having the same issue.

I solved it by adding a __del__ method that terminates the subprocess.

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Answer