problem with pipes Post: 302239121

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Top Forums UNIX for Dummies Questions & Answers problem with pipes Post 302239121 by afser on Tuesday 23rd of September 2008 02:22:02 AM

09-23-2008

Registered User

problem with pipes

I have written the following program. The function of this prog is to read data from a file(source.c) and write into another file(dest.c) using pipes. I have just written a line in the source file.Im able to compile and run the program without errors. But the data is not written onto the other file(dest.c);
please help!!!!!!!!!!!!!!!!!!!!!!

[code]

#include <sys/wait.h>
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

int main()
{
int pfd[2],i=0,j=0;;
pid_t cpid;
char buf[20],ch,c;
FILE *fp1,*fp2;

fp1=fopen("source.c","r+");
if(fp1==NULL)
{
perror("Error opening source file\n");
}
while((ch=getc(fp1))!=EOF)
{
buf[i]=ch;
printf("i=%d ch=%c\n",i,ch);
i++;
}
buf[i] = '\0';
fclose(fp1);

if (pipe(pfd) == -1)
{
perror("pipe");
exit(EXIT_FAILURE);
}

cpid = fork();
if (cpid == -1)
{
perror("fork");
exit(EXIT_FAILURE);
}

if (cpid == 0)
{ /* Child reads from pipe */
char arr;
close(pfd[1]); /* Close unused write end */
fp2=fopen("dest.c","w+");
if(fp2==NULL)
{
perror("Error opening dest file\n");
_exit(1);
}
int i = 0;
while (i<=19)
{
read(pfd[0], &buf[i], sizeof(buf[i]));
c=buf[i];
putc(c,fp2);
i++;
}
close(pfd[0]);
_exit(EXIT_SUCCESS);
}
else
{ /* Parent writes argv[1] to pipe */
j=0;
close(pfd[0]); /* Close unused read end */
write(pfd[1], buf, strlen(buf));
j++;
close(pfd[1]); /* Reader will see EOF */
wait(NULL); /* Wait for child */
exit(EXIT_SUCCESS);
}
fclose(fp2);
}

afser

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LEARN ABOUT FREEBSD

pipe2

PIPE(2) 						      BSD System Calls Manual							   PIPE(2)

NAME

     pipe, pipe2 -- create descriptor pair for interprocess communication

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     pipe(int fildes[2]);

     int
     pipe2(int fildes[2], int flags);

DESCRIPTION

     The pipe() system call creates a pipe, which is an object allowing bidirectional data flow, and allocates a pair of file descriptors.

     The pipe2() system call allows control over the attributes of the file descriptors via the flags argument.  Values for flags are constructed
     by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

     O_CLOEXEC	 Set the close-on-exec flag for the new file descriptors.

     O_NONBLOCK  Set the non-blocking flag for the ends of the pipe.

     If the flags argument is 0, the behavior is identical to a call to pipe().

     By convention, the first descriptor is normally used as the read end of the pipe, and the second is normally the write end, so that data
     written to fildes[1] appears on (i.e., can be read from) fildes[0].  This allows the output of one program to be sent to another program: the
     source's standard output is set up to be the write end of the pipe, and the sink's standard input is set up to be the read end of the pipe.
     The pipe itself persists until all its associated descriptors are closed.

     A pipe that has had an end closed is considered widowed.  Writing on such a pipe causes the writing process to receive a SIGPIPE signal.
     Widowing a pipe is the only way to deliver end-of-file to a reader: after the reader consumes any buffered data, reading a widowed pipe
     returns a zero count.

     The bidirectional nature of this implementation of pipes is not portable to older systems, so it is recommended to use the convention for
     using the endpoints in the traditional manner when using a pipe in one direction.

RETURN VALUES

     The pipe() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate
     the error.

ERRORS

     The pipe() and pipe2() system calls will fail if:

     [EMFILE]		Too many descriptors are active.

     [ENFILE]		The system file table is full.

     [ENOMEM]		Not enough kernel memory to establish a pipe.

     The pipe2() system call will also fail if:

     [EINVAL]		The flags argument is invalid.

SEE ALSO

     sh(1), fork(2), read(2), socketpair(2), write(2)

HISTORY

     The pipe() function appeared in Version 3 AT&T UNIX.

     Bidirectional pipes were first used on AT&T System V Release 4 UNIX.

     The pipe2() function appeared in FreeBSD 10.0.

BSD
								    May 1, 2013 							       BSD

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