CODEWITHSUNDEEP
clinux
BEPP
BEPP

Reputation: 955

read & write system call returns 1 always

I need to copy content of one file to another. But the problem is I am getting the read & write return value as always 1. But in buffer data is read. Can someone please explain what going wrong here? I am using gcc compiler.

#include<stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include<string.h>
int copy_file_to_file(int,int);
int main()
{
    int src_fd,dst_fd;
    if ( (src_fd = open("source.txt",O_RDONLY)) == -1 )
    {
       printf("file opening error");
       return -1;
    }
    if( (dst_fd = open("destination.txt",O_WRONLY | O_CREAT,0644)) == -1 )
   {
       printf("destination file opening error\n");
       return -1;
   }
   copy_file_to_file(src_fd,dst_fd);
   close(src_fd);
   close(dst_fd);
   return 0;
}

int copy_file_to_file(int source_fd,int dest_fd)
{
    int byte_read, byte_write;
    char buf[10];

    while((byte_read = read(source_fd, buf, 10)>0) )
   {

      byte_write=write(dest_fd, buf, byte_read);
      printf("buf=%s byte_read = %d byte_write=%d \n",buf,byte_read,byte_write);
   }
  return 0;
}

output:-

buf=Hello world

I am working byte_read = 1 byte_write=1

Upvotes: 0

Views: 1381

Answers (1)

bolov
bolov

Reputation: 75727

while((byte_read = read(source_fd, buf, 10)>0) )

is interpreted as (br = (read() > 0))

fix:

while((byte_read = read(source_fd, buf, 10)) > 0)

Operator precedence

Upvotes: 9

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