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Writing c code for who | sort | lp
Post 302123711 by the_learner on Tuesday 26th of June 2007 09:12:38 PM
06-26-2007
Quote:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
int pipe1[2]; /* pipe for: sort ------> uniq */
int pipe2[2]; /* pipe for: uniq ------> wc */
int pipe3[2]; /* pipe for: read result from wc */
void
close_des()
{
close(pipe1[0]);
close(pipe1[1]);
close(pipe2[0]);
close(pipe2[1]);
close(pipe3[0]);
close(pipe3[1]);
}
int main()
{
u_long uniqLines;
pid_t pid;
int status;
pipe(pipe1);
pid = fork();
if(pid == 0) {
/*
* Child Process - sort
*/
dup2(pipe1[1],1);
close_des();
execlp("sort","sort","work.fp",NULL);
} else {
/*
* Parent Process
*/
pipe(pipe2);
if (!fork()) {
/*
* uniq
*/
dup2(pipe1[0],0);
dup2(pipe2[1],1);
close_des();
execlp("uniq","uniq","-c",NULL);
} else {
pipe(pipe3);
if (!fork()) {
dup2(pipe2[0],0);
dup2(pipe3[1],1);
close_des();
execlp("wc","wc","-l",NULL);
} else {
dup2(pipe3[0],0);
close_des();
scanf("%lu",&uniqLines);
}
}
..... and so on ....
}Quote:
Code:
int main()
{
int pipe1[2]; /* pipe for: sort ------> uniq */
int pipe2[2]; /* pipe for: uniq ------> wc */
int pipe3[2]; /* pipe for: read result from wc */
u_long uniqLines;
pid_t pid;
int status;
pipe(pipe1);
fcntl(pipe1[0],F_SETFD,FD_CLOEXEC);
fcntl(pipe1[1],F_SETFD,FD_CLOEXEC);
pid = fork();
if(pid == 0) {
/*
* Child Process - sort
*/
dup2(pipe1[1],1);
execlp("sort","sort","work.fp",NULL);
} else {
/*
* Parent Process
*/
pipe(pipe2);
fcntl(pipe2[0],F_SETFD,FD_CLOEXEC);
fcntl(pipe2[1],F_SETFD,FD_CLOEXEC);
if (!fork()) {
/*
* uniq
*/
dup1(pipe1[0],0);
close(1);
dup(pipe2[1]);
execlp("uniq","uniq","-c",NULL);
} else {
pipe(pipe3);
fcntl(pipe3[0],F_SETFD,FD_CLOEXEC);
fcntl(pipe3[1],F_SETFD,FD_CLOEXEC);
if (!fork()) {
/*
* wc
*/
dup2(pipe2[0],0);
dup(pipe3[1],1);
execlp("wc","wc","-l",NULL);
} else {
dup2(pipe3[0],0);
fprintf(stderr, "\n reached after wc");
scanf("%lu",&uniqLines);
}
}In both the occasion..the code seems to hang.. I dont know why..
But for some cases, if I leave some of the close statements in there.. it seems to work..
I really dont understand this pipe() and fork() and dup() and fnctl()... I think I need to buy that book which Perderabo suggested.. Advanced Unix Programming..
But I need to get this done urgently
Porter please help...|
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