Using asynchoronous I/O : readv and writev

Hi,
I am trying to write a program to copy files using aync I/O in unix.
I have written this code :

Code:

---

#include<stdio.h>
#include<sys/types.h>
#include<sys/uio.h>
#include<unistd.h>

int main(int argc,char *argv[])
{
        int fs,fd;
        ssize_t bytes_read,bytes_written;
        char buf[3][50];
        int iovcnt;
        struct iovec iov[3];
        int i;
        fs=open(argv[1],O_RDONLY);
        fd=open(argv[2],O_RDWR | O_CREAT);
        for(i=0;i<3;i++)
        {
                iov[i].iov_base=buf[i];
                iov[i].iov_len=sizeof(buf[i]);
        }
        iovcnt=sizeof(iov)/sizeof(struct iovec);
        while((bytes_read=readv(fs,iov,iovcnt))!=-1)                         
                if((bytes_written=writev(fd,iov,iovcnt))==-1)
                        printf("Write error\n");
        close(fs);
        close(fd);
        return 0;
}

---

The contents of source file are getting copied to the destination but some junk is also appended with it. I suspect the problem is because of the buffers used for writing. The extra space in the buffers have junk which is written to the file. Can anyone suggest a fix for this?

You need to adjust the I/O vectors so that they don't claim to contain sizeof(buf[i]) bytes when they only contain a total of bytes_read bytes.

Why the scatter/gather operation anyway?

Oh yeah, that's not asynchronous I/O, by the way. That's perfectly synchronous. Only the scatter/gather operation is different from a simple read/write loop. And it only makes things difficult for you.