Interprocess Communication

[Zildjian]

Hello,

I am currently writing a program to create two processes and then have them communicate using a pipe. Here is my code:

#include <stdio.h>

int main() {
    int pid, processes[2];
    int fork();
    
    pipe(processes);
    
    pid = fork();
    
    if (pid == 0) {
        close(processes[0]);
        char buf[BUFSIZ];
        
        char message[] = "Hi, this pid 0. Here is something for you!";
        printf("Sending message: %s\n",message);
        write(processes[1],message, strlen(message)+1);
        printf("pid %d send completed\n", pid);
    }
    else {
        close(processes[1]);
        char buf[BUFSIZ];
        
        while ( read(processes[0],buf,BUFSIZ) > 0 )
            printf("pid %d received message: %s \n",pid,buf);
            
    }
}

This succeeds in sending a message one way, but how would I go about sending both ways? Basically, what I want to do is have the process that reads the message be able to send a reply back to the process it received the message from. Also, how would I get the time that the message was sent at? I have tried a number of different things to get both of these to work and none have done so. Any help would be greatly appreciated. Thanks.

[Salem]

> but how would I go about sending both ways?
Create another pipe of course

> Also, how would I get the time that the message was sent at?
Depends what you mean by time
Wall-clock time you get using the time() function.

[Zildjian]

Ok, I've looked up how to use the time() function and I can't seem to figure it out. Could you show me how I would go about using it in the context of my program? I tried to use and got a really huge number.

[Perspective]

> but how would I go about sending both ways?
Create another pipe of course

this is the best (and most portable) solution. but if your using a sun box you could just use the same pipe both ways! (full-duplex pipes)

[Salem]

C'mon, just read the manual pages
They all give you "see also" sections which list related functions, just follow through a bit.

struct tm *gmtime(const time_t *timep);
struct tm *localtime(const time_t *timep);
Convert a time_t into a struct tm

char *asctime(const struct tm *tm);
Produces a nice printable string

size_t strftime(char *s, size_t max, const char *format,
const struct tm *tm);
Same as asctime(), but with lots of formatting controls along the line of printf