Inverting a string using `fork()`

Question

I'm trying to invert a string in C++ using fork(), such that each process prints at most one character. My thinking is that after printing each character, I fork into a new process, end the parent process, and continue. Here is my code:

#include <string>
#include <iostream>
#include <unistd.h>

/*
    Recursively print one character at a time,
    each in a separate process.
*/
void print_char(std::string str, int index, pid_t pid)
{
    /*
        If this is the same process, 
        or the beginning of the string has been reached, quit.
    */
    if (pid != 0 || index <= -1)
      return;

    std::cout << str[index];
    if (index == 0)
    {
        std::cout << std::endl;
        return;
    }
    print_char(str, index-1, fork());
}

int main(int argc, char** argv)
{
    std::string str(argv[1]);
    print_char(str, str.length()-1, 0);
}

However, when testing the code with the argument "hey", it prints "yeheyy". My understanding of fork() is that it creates a duplicate process with a copy of the memory space, and whenever I mentally "walk through" the code it seems like it should work, but I cannot figure out where my logic is failing.

There are fairly better and easier methods to invert a string. — user0042
– user0042, Commented Oct 2, 2017 at 5:11
You’re probably going to need to use wait() or one of its relatives. The first process needs to fork a child that will print the rest of the string, and wait for it to complete before printing its character (and a newline). I’ll also observe that I cannot think of a circumstance where I’d use fork() as a parameter to a function call. — Jonathan Leffler
– Jonathan Leffler, Commented Oct 2, 2017 at 5:13

Kajienk · Accepted Answer · 2017-10-02 05:11:49Z

2

It seems, your code is OK, but you have trouble with cout.

try change only the output line

std::cout << str[index];

with

std::cout << str[index] << std::flush;

tried it and worked for me.

answered Oct 2, 2017 at 5:11

Kajienk

1111 silver badge4 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Inverting a string using `fork()`

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related