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Parent,child wait,signal


 
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# 15  
Old 06-06-2011
So, read takes the bytes partially? i should put more read functions underneath?
# 16  
Old 06-07-2011
It can take bytes partially but I have no idea if that's the case right now because
a) You haven't posted enough of the program
b) You haven't checked read's return value
c) You're feeding the array into printf("%s") which expects strings, even though
c) read doesn't read strings! It puts no null terminator in it for you! Use write or fwrite!
# 17  
Old 06-07-2011
Corona,

Till now i was considering that pipes and fifo are same except the fact that fifo's existence can be control since it has a name and sometimes resides in a file system.

But now i have doubt, is there any other difference between them considering implementation and usage.

This is what i was referring to
Quote:
A pipe is a mechanism for interprocess communication; data written to the pipe by one process can be read by another process. The data is handled in a first-in, first-out (FIFO) order. The pipe has no name; it is created for one use and both ends must be inherited from the single process which created the pipe.
A FIFO special file is similar to a pipe, but instead of being an anonymous, temporary connection, a FIFO has a name or names like any other file. Processes open the FIFO by name in order to communicate through it.
# 18  
Old 06-07-2011
Ok i ll send you everything in case you understand what is hhappening. I do everything as i saw it online.I keep getting an Input/Output error on read.

Code:
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>
#include <sys/wait.h>
#include  <stdio.h>
#include  <signal.h>
#include  <sys/ipc.h>
#include  <sys/shm.h>
#define MAX_BUF 5000

int main(int argc, char **argv)
{
    pid_t pid;
    int i,fd;
    char buf[MAX_BUF]="",data[MAX_BUF]="";
    char * myfifo = "/cygdrive/c/a/progsys/tmp";
     if (mkfifo(myfifo, 0666) != 0)
        perror("mkfifo() error");
    for(i=1;i<5;i++)
    {
        strcat(data,argv[i]);
        strcat(data," ");    
    }
    fprintf(stderr,"#%s#",data);
    pid = fork();
    if (pid == -1) 
    { 
        perror("Can't create child\n");
        exit(1);
    }
    else 
        if (pid == 0) 
        {
   
            if(execl("b.exe","b.exe",NULL) == -1)
                fprintf(stderr,"execl Error!\n");
        }
        else 
            {
                if(fd = open(myfifo, O_WRONLY)<0)  perror("open() error for read end");
                   if (write(fd, data, strlen(buf))<0);    perror("write() error");
                printf("Parent ended ");
                close(fd);
                fd = open(myfifo, O_RDONLY);
            }
}

Child
Code:
#include <stdlib.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>
#include <sys/wait.h>
#include  <stdio.h>
#include  <signal.h>
#include  <sys/ipc.h>
#include  <sys/shm.h>
#define MAX_BUF 5000

int main(int argc, char **argv)
{
    int fd,i,j,iteration=1,lowerBound,upperBound,numPoints,numread;
    char * myfifo = "/cygdrive/c/a/progsys/tmp";
    char buf[MAX_BUF]="",permbuf[MAX_BUF]="",sourcefile[MAX_BUF]="",finalsourcefile[MAX_BUF]="";
    if (fd = open(myfifo, O_RDONLY)<0) perror("open() error for read end");
    sleep(5);
    if (numread=read(fd, buf, sizeof(MAX_BUF))<0) perror("read ferror for read end");
    buf[numread]='0';
    write (1,buf,numread);

# 19  
Old 06-07-2011
Lots of errors.

Code:
char * myfifo = "/cygdrive/c/a/progsys/tmp";

I repeat: fifo's might not work on Windows, because windows doesn't even have them. The closest it has is a named pipe that doesn't actually exist as a file anywhere.
Quote:
if (mkfifo(myfifo, 0666) != 0)
perror("mkfifo() error");
You don't actually quit after most errors.
Code:
fprintf(stderr,"#%s#\n",data);

Unless you really want to view everything as one giant messy line, you might want to put an \n in things once in a while.
Code:
        if (pid == 0) 
        {
   
            if(execl("b.exe","b.exe",NULL) == -1)
                fprintf(stderr,"execl Error!\n");

            exit(1);

Can't forget that. If b.exe fails to run for any reason, the child will keep going!
Code:
                   if (write(fd, data, strlen(buf))<0);    perror("write() error");

That extra semicolon means it will always print 'write error', even when there's no write error.
Code:
                printf("Parent ended ");
                close(fd);
                fd = open(myfifo, O_RDONLY);

Why is the parent opening the fifo twice? The child doesn't open it twice, the parent will wait forever for something to open it again.

Why do you have your child code in a separate program when you could put it all in one and save yourself a lot of headaches?
Code:
buf[numread]='0';

0 is not null, 0 is 0. Try '\0'.
Code:
write (1,buf,numread);

...not that you actually need a null terminator any more when you use write(). How about fprintf(stderr, "%d bytes\n", (int)numread); to see how many you actually read?

---------- Post updated at 09:29 AM ---------- Previous update was at 09:19 AM ----------

Lastly: Your main program is writing 0 bytes on purpose because you're checking the length of the wrong buffer -- buf, instead of data.

---------- Post updated at 09:33 AM ---------- Previous update was at 09:29 AM ----------

Also: sizeof(MAX_BUFFER) is probably 4 or 8, not 5000 like you intended. Just MAX_BUFFER is what you want.

---------- Post updated at 09:38 AM ---------- Previous update was at 09:33 AM ----------

Also if(fd = open(myfifo, O_WRONLY)<0) doesn't have enough brackets. fd becomes either 0 or 1 -- which is never the FD of your open fifo! You've been reading from stdin and writing to stdin, not your fifo, I think.

When I correct all that, it works fine, with no sleep().

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