Pipe Usage In C - c

Question

I have a question on usage pipes in C. I want have a multidimensional array in main process. This array stores 24 lines of text and a line contains 256 byte (BUFFER). Here is my code.
BUFFER SIZE DEFINED ON TOP = 256 BYTE
READ_END DEFINED ON TOP = 0
WRITE END DEFINED ON TOP = 1
char buffer[BUFFER_SIZE];
char *read_msg[100];
char *write_msg[100];
FILE *fp;
fp = fopen(argv[1], "r");
pid_t pid;
int fd[2];
pid = fork();
if (pid < 0) { // error
fprintf(stderr, "Fork Failed");
return 1;
}
if (pid == 0) { // child process does the time consuming task
close(fd[WRITE_END]);
read(fd[READ_END], &read_msg, 24*BUFFER_SIZE);
close(fd[READ_END]);
for (int i = 0; i < 24; ++i) {
printf("Received string: %s\n", read_msg[i]);
}
}
if (pid > 0) { // parent is responsive immediately
for (int i = 0; i < 24; ++i) {
if (fgets(buffer, sizeof(buffer), fp)) {
write_msg[i] = malloc(sizeof(buffer) + 1);
strcpy(write_msg[i], buffer);
}
}
close(fd[READ_END]);
write(fd[WRITE_END], &write_msg, 24*BUFFER_SIZE);
close(fd[WRITE_END]);
}
}
}
In child process, i want to print these lines but it prints nothing. How can i fix it? Thanks...
SOLUTION
char buffer[BUFFER_SIZE];
char read_msg[100][BUFFER_SIZE];
char write_msg[100][BUFFER_SIZE];
FILE *fp;
fp = fopen(argv[1], "r");
pid_t pid;
int fd[2];
pipe(fd);
pid = fork();
if (pid < 0) { // error
fprintf(stderr, "Fork Failed");
return 1;
}
if (pid == 0) {
close(fd[WRITE_END]);
read(fd[READ_END], &read_msg, 24*BUFFER_SIZE);
close(fd[READ_END]);
for (int i = 0; i < 24; ++i) {
printf(read_msg[i]);
}
}
if (pid > 0) {
for (int i = 0; i < 24; ++i) {
if (fgets(buffer, sizeof(buffer), fp)) {
strcpy(write_msg[i], buffer);
}
}
close(fd[READ_END]);
write(fd[WRITE_END], &write_msg, 24*BUFFER_SIZE);
close(fd[WRITE_END]);
}
}
}

Answer 1

I forgot to write pipe(fd) before fork(). Thank you all :)