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Top Forums Programming read and write stdin/stdout in unix Post 302414793 by MrUser on Wednesday 21st of April 2010 03:31:08 AM
Old 04-21-2010
read and write stdin/stdout in unix

Hi,
i am using the below program to read from the standard input or to write to standard out put.

i know that using highlevel functions this can be done better than what i have done here.

i just want to know is there any other method by which i find the exact number of characters ( this will vary in each iteration ) , and write that to STDOUT.

this process i want to terminate with a press of "q".

does read syscall stores the null at the end of string, i have not found that in debug mode.

below is the sample code but its has got the problem of reading and writing garbages.


Code:
#include<unistd.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include <stdio.h>
#include<string.h>

int main( void )
{
        char buf[20];

        while( 1 )
        {
                       read(STDIN_FILENO , buf ,  sizeof( buf ));
                       write(STDOUT_FILENO, buf , strlen( buf ));

                if(!strcmp(buf,"q\n"))
                        break;
        }

        return 0;
}

 

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SRV(3)							     Library Functions Manual							    SRV(3)

NAME
srv - server registry SYNOPSIS
bind #s /srv #s/service1 #s/service2 ... DESCRIPTION
The srv device provides a one-level directory holding already-open channels to services. In effect, srv is a bulletin board on which pro- cesses may post open file descriptors to make them available to other processes. To install a channel, create a new file such as /srv/myserv and then write a text string (suitable for strtoul; see atof(2)) giving the file descriptor number of an open file. Any process may then open /srv/myserv to acquire another reference to the open file that was reg- istered. An entry in srv holds a reference to the associated file even if no process has the file open. Removing the file from /srv releases that reference. It is an error to write more than one number into a server file, or to create a file with a name that is already being used. EXAMPLE
To drop one end of a pipe into /srv, that is, to create a named pipe: int fd, p[2]; char buf[32]; pipe(p); fd = create("/srv/namedpipe", 1, 0666); sprint(buf, "%d", p[0]); write(fd, buf, strlen(buf)); close(fd); close(p[0]); write(p[1], "hello", 5); At this point, any process may open and read /srv/namedpipe to receive the hello string. Data written to /srv/namedpipe will be received by executing read(p[1], buf, sizeof buf); in the above process. SOURCE
/sys/src/9/port/devsrv.c SRV(3)
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