help me with piping...

[haj1st]

I've started to learn c programing 2 weeks ago (i have gone to class tree times) and our instructor gave us a homework...
and I have to submit it for the next week ...
I have to mention that the biggest program I have written with c is: " hello world!!!"
he said that copy the content of a.txt to b.txt by using pipes...and I don't know any thing about piping yet and i didn't find any thing useful on the web,and I want to know how should I use piping in windows?!!...

[haj1st]

by the way excuse my english...

[samf]

Piping after only two weeks of class? I find it hard to believe that a more advanced subject is being given so early in a course. Are you sure your instructor said to use piping in a 'C' program? You can use piping from the command line, which is probably what the instructor meant. There is something missing from your story that you haven't told us. Is this an 'Intro to C' course or a more advanced course?

[haj1st]

Piping after only two weeks of class? I find it hard to believe that a more advanced subject is being given so early in a course. Are you sure your instructor said to use piping in a 'C' program? You can use piping from the command line, which is probably what the instructor meant. There is something missing from your story that you haven't told us. Is this an 'Intro to C' course or a more advanced course?

last term I passed python and this term we're going to master c...

[samf]

It doesn't matter what you took previously. A first class in a new language does not usually begin with piping until you have mastered other basic concepts like conditions, looping, etc.

If you are willing to tackle this more advanced topic, try this...

Cprogramming.com FAQ > Working with Processes

[haj1st]

thanx , but it's a little bit confusing, I just want to copy a text file to another by editing the following code and also using pipes:

int c;
while((c=getchar())!=EOF){
    putchar(c);
}

[haj1st]

It doesn't matter what you took previously. A first class in a new language does not usually begin with piping until you have mastered other basic concepts like conditions, looping, etc.

If you are willing to tackle this more advanced topic, try this...

Cprogramming.com FAQ > Working with Processes

thanx , but it's a little bit confusing, I just want to copy a text file to another by editing the following code and also using pipes:

[Memloop]

Pipes are not part of standard C, so I don't see why an introductory course to C should even mention them.

[samf]

Does your instructor mean for you to create a program that would take a file and send the output to stdout? Most programs that can accept stdin data can have its data piped into it via shell commands like so:

$ cat file.dat
Apple 1.1
Apple 1.5
Apple 1.9
Banana 1.3
Banana 2.7
Banana 3.3

$ cat file.dat | grep Banana
Banana 1.3
Banana 2.7
Banana 3.3

The '|' is the piping symbol that takes stdout from the previous program and funnels it into the stdin in of the program on the right side of the '|' symbol.

If this is similar to what you want, all you have to do is use putchar to write the contents of the file to stdout, which it seems you are already doing. You now have to use getchar to read the file and use putchar to send it to stdout.

[bigbug]

seems that there are some classmates of mine over here...

[karthigayan]

Ya,it is a advanced concept.But easy to understand.

Pipe is half duplex.In c we can achieve the pipe by using the function pipe().It internally uses fork.I think you may aware of fork.It will create a new process.

Pipe() will return two descriptors.one descriptor fd[0] is for reading and another descriptor fd[1] for writing.So if you write in the write end and you can read that in another end.For your requirement you just read from the source file and write that data it in the fd[1] (write end) then read that in the read end then you just write the data in the destination file.

To know in detail refer : man pipe .

I tried the requirement

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include<fcntl.h>
#include<stdlib.h>

#define MAXSIZE 1024
main()
{
        int     fd[2];
        pid_t   childpid;
        int f_desc,f_desc1,n;
        char buf[MAXSIZE];

        pipe(fd);

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

        if(childpid == 0)
        {
                close(fd[1]);
                if((n=read(fd[0],buf,MAXSIZE))!=-1)
                {
                        if((f_desc1=open("backup",O_CREAT|O_RDWR,0644))!=1)
                        {
                                write(f_desc1,buf,n);
                        }
                        else
                        {
                                printf("open : error \n");
                        }
                }
                        else
                        {
                                printf("read error");
                        }
                }
                else
                {
                        close(fd[0]);
                        if((f_desc=open("a.c",O_RDONLY))!=-1)
                        {
                                if((n=read(f_desc,buf,MAXSIZE))!=-1)
                                {
                                        write(fd[1],buf,n);
                                }
                                else
                                {
                                        printf("read error");
                                }
                        }
                        else
                        {
                                printf("open : error \n");
                        }
                }
        }