In C++, calling fork when cin is a bash heredoc causes repeated input fragments
I was able to reproduce this problem, not only using the heredoc but also using a standard file redirection.
Here is the test script that I used. In both the first and second cases, I got a duplication of the second line of input.
./a.out < Input.txtechocat Input.txt | ./a.outecho./a.out <<EOFhello worldgoodbye worldEOFClosing the stdin before exiting in the child seems to eliminate both of the problems.
#include <iostream>#include <sstream>#include <unistd.h>#include <sys/wait.h>#include <limits>int main(int argc, char **argv){ std::string line; while (std::getline(std::cin, line)) { pid_t pid = fork(); if (pid == 0) { // child close(STDIN_FILENO); break; // exit after first closing stdin } else if (pid > 0) { // parent waitpid(pid, nullptr, 0); } else { // error perror("fork"); } std::cout << getpid() << ": " << line << "\n"; } return 0;}