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copied!<p>Actually, after struggling with it a bit, it seems like the only solution to this problem is by making the 'parent' process pretending to be a terminal using the OS pseudo terminal API calls.</p> <p>One should call 'openpty()' before the fork(), and inside the child code, he should call 'login_tty(slave)' the slave is then becoming the stdin/out and stderr.</p> <p>By pretending to a terminal, the buffering of stdout is automatically set to 'line mode' (i.e. flush occurs when \n is encountered). The parent should use the 'master' descriptor for readin/writing with the child process.</p> <p>The modified parent code (in case anyone will ever need this):</p> <pre><code>#include <unistd.h> #include <signal.h> #include <sys/types.h> #include <sys/select.h> #include <errno.h> #include <sys/wait.h> #include <string> #include <string.h> #include <cstdio> #include <pty.h> #include <utmp.h> static int read_handle(-1); static pid_t pid; bool read_from_child(std::string& buff) { fd_set rs; timeval timeout; memset(&rs, 0, sizeof(rs)); FD_SET(read_handle, &rs); timeout.tv_sec = 1; // 1 second timeout.tv_usec = 0; int rc = select(read_handle+1, &rs, NULL, NULL, &timeout); if ( rc == 0 ) { // timeout return true; } else if ( rc > 0 ) { // there is something to read char buffer[1024*64]; // our read buffer memset(buffer, 0, sizeof(buffer)); if(read(read_handle, buffer, sizeof(buffer)) > 0) { buff.clear(); buff.append( buffer ); return true; } return false; } else { /* == 0 */ if ( rc == EINTR || rc == EAGAIN ) { return true; } // Process terminated int status(0); waitpid(pid, &status, 0); return false; } } void execute() { char *argv[] = {"/home/eran/devl/TestMain/Debug/TestMain", NULL}; int argc = 1; int master, slave; openpty(&master, &slave, NULL, NULL, NULL); int rc = fork(); if ( rc == 0 ) { login_tty(slave); close(master); // execute the process if(execvp(argv[0], argv) != 0) perror("execvp"); } else if ( rc < 0 ) { perror("fork"); return; } else { // Parent std::string buf; close(slave); read_handle = master; while(read_from_child(buf)) { if(buf.empty() == false) { printf("Received: %s", buf.c_str()); } buf.clear(); } } } int main(int argc, char **argv) { execute(); return 0; } </code></pre>

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