int main()
{
int pipefd[2];
char buf;
int pid, pid1;
pid = fork();
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
if(pid == 0){ // CHILD 1
close(pipefd[1]);
while(read(pipefd[0],&buf,1) > 0){ // THIS DOESNT WORK
printf("FIRST CHILD WRITES: %s\n",&buf); // THIS DOESNT WORK
} // THIS DOESNT WORK
close(pipefd[0]);
_exit(EXIT_SUCCESS);
}else{
pid1 = fork();
if(pid1 == 0){ // CHILD 2
close(pipefd[1]);
// while(read(pipefd[0],&buf,1) > 0){ // ONLY THIS (WOULD) WORK
// printf("SECOND CHILD WRITES: %s\n",&buf); // ONLY THIS (WOULD) WORK
// } // ONLY THIS (WOULD) WORK
close(pipefd[0]);
_exit(EXIT_SUCCESS);
}else{ // PARENT
close(pipefd[0]);
char* s = "Write To Pipe";
write(pipefd[1],s,strlen(s));
close(pipefd[1]);
wait(NULL); // WAIT FOR CHILD TO TERMINATE
wait(NULL); // WAIT FOR CHILD TO TERMINATE
}
}
return 0;
}
Whenever I try to run the program only the 2ND CHILD can read from the pipe, the 1ST CHILD never. So I tried commenting the second child's pipe reading, however the first child still can't read from the pipe to which the parent wrote into.
Why can't the 1ST CHILD read from the pipe?
Thanks for the help!
The order is wrong. Your code is
pid = fork();
if (pipe(pipefd) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
You need to create the pipe before you fork. You would probably catch this type of error if you check for errors on the close and/or the read.
But this demonstrate why is is best practice to always check for errors, even on functions that you know will work.
No, this particular error would not be caught by noticing a failure on close(). But it's a good idea to check, since that will catch errors in which the file descriptor is otherwise invalid.