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#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
static int split(int fd[2]);
static int redir(int fd, const char* file);
static void sig_handler(int sig);
static int parent;
int main(void) {
ssize_t bytes;
char buf[256];
int fd[2];
// disable buffering for stdout
setvbuf(stdout, NULL, _IONBF, 0);
// redirect stdout to write into a file
if (redir(1, "log.txt") < 0) {
perror("redir()");
exit(-1);
}
// install the signal handler for Ctrl+C
if (signal(SIGINT, sig_handler) == SIG_ERR) {
perror("signal()");
exit(-1);
}
// split processes and assign file descriptors for communication
switch (split(fd)) {
case -1: // error
exit(-1);
case 0: // child
while ((bytes = read(fd[0], buf, sizeof(buf))) > 0) {
printf("[%u]: %s\n", getpid(), buf);
sleep(1);
write(fd[1], "pong", 5);
}
break;
case 1: // parent
parent = 1;
write(fd[1], "ping", 5);
while ((bytes = read(fd[0], buf, sizeof(buf))) > 0) {
printf("[%u]: %s\n", getpid(), buf);
sleep(1);
write(fd[1], "ping", 5);
}
break;
}
// close the file descriptors
close(fd[0]);
close(fd[1]);
return 0;
}
int split(int fd[2]) {
int pfd[2][2];
if (pipe(pfd[0]) < 0) {
perror("pipe()");
goto err_pipe1;
}
if (pipe(pfd[1]) < 0) {
perror("pipe()");
goto err_pipe2;
}
switch (fork()) {
case -1:
perror("fork()");
goto err_fork;
case 0: // child process
close(pfd[0][1]); // close write for child
close(pfd[1][0]); // close read for parent
fd[0] = pfd[0][0]; // keep read for child
fd[1] = pfd[1][1]; // keep write for parent
return 0;
default: // parent process
close(pfd[1][1]); // close write for parent
close(pfd[0][0]); // close read for child
fd[0] = pfd[1][0]; // keep read for parent
fd[1] = pfd[0][1]; // keep write for child
return 1;
}
err_fork:
close(pfd[1][0]);
close(pfd[1][1]);
err_pipe2:
close(pfd[0][0]);
close(pfd[0][1]);
err_pipe1:
return -1;
}
int redir(int fd, const char* file) {
int fd2 = open(file, O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fd2 < 0)
return -1;
dup2(fd2, fd);
close(fd2);
return 0;
}
void sig_handler(int sig) {
if (parent) {
const char msg[] = "Programmabbruch durch Nutzer\n";
write(1, msg, sizeof(msg) - 1);
}
exit(0);
}
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