Sending C Command Line Arguments Through Pipe - c

Question

I am trying to send my command line arguments through from the child process to the parent process using a pipe but can't figure out what I'm doing wrong. My code is below. Any help is appreciated. Thanks in advance.
int main(int argc, char argv[])
pid_t child;
int fd[2];
pipe(fd);
if((child = fork() == 0)
{
int len = strlen(argv[1]);
close(fd[0];
write(fd[1], argv[1], len);
exit(0);
}
else //Assuming process won't fail for now
{
char src[10]; //Just using 10 for now, no arguments have more than 10 characters
read(fd[0], src, (strlen(src)));
fprintf(stderr, "%s\n", src);
close(fd[0]);
}
}

Answer 1

You had a bunch of little errors but as far as I can see, believe it or not, this may be your real problem.
read(fd[0], src, (strlen(src)));
My guess is that the first char is null and you are successfully reading 0 bytes.
Change to
read(fd[0], src, (sizeof(src)));
In your larger project make sure you read and write in loops. You are not guaranteed to read or write what you specify.

Answer 2

You may need to close fd[1] inside the else block first.
check this example
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
int
main(int argc, char *argv[])
{
int pipefd[2];
pid_t cpid;
char buf;
if (argc != 2) {
fprintf(stderr, "Usage: %s <string>\n", argv[0]);
exit(EXIT_FAILURE);
}
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
cpid = fork();
if (cpid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (cpid == 0) { /* Child reads from pipe */
close(pipefd[1]); /* Close unused write end */
while (read(pipefd[0], &buf, 1) > 0)
write(STDOUT_FILENO, &buf, 1);
write(STDOUT_FILENO, "\n", 1);
close(pipefd[0]);
_exit(EXIT_SUCCESS);
} else { /* Parent writes argv[1] to pipe */
close(pipefd[0]); /* Close unused read end */
write(pipefd[1], argv[1], strlen(argv[1]));
close(pipefd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
}

Answer 3

You have assumed that fork() will not fail.
But what about pipe()??
Assume both get completed successfully, then closing fds properly is requered.
your if-else blocks should be like this.
if((child = fork() == 0)
{
int len = strlen(argv[1]);
close(fd[0]);//I assume this was your typo. otherwise it would not even get compiled
write(fd[1], argv[1], len);
close(fd[1]);
exit(0);
}
else //Assuming process won't fail for now
{
close(fd[1]);
char src[10]; //Just using 10 for now, no arguments have more than 10 characters
read(fd[0], src, (strlen(src)));
fprintf(stderr, "%s\n", src);
close(fd[0]);
}