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Question

Hi I am trying to read from a file and print it on terminal. But fwrite() does not print anything. Can anyone please help! I cannot see the output from the file on the terminal. After debugging all I can see is program is not entering into while loop used before fwrite() .

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

#define BUF_SIZE 128

int main(int argc, char* argv[]) 
{
    int BATT_fd, ret_write, ret_read, i;
    char buffer[BUF_SIZE];      

    if(argc != 2)
    {
        printf ("\nUsage: cp file1 file2\n");
        return 1;
    }

    BATT_fd = open (argv [1], O_RDWR | O_CREAT, S_IRWXU);

    if (BATT_fd == -1) 
    {
        perror ("open");
        return 2;
    }

 printf("\n file opened successfully with file desc %d\n", BATT_fd);
 printf("enter data into file\n");
 scanf("%[^\n]", buffer);

     if((ret_write = write (BATT_fd, &buffer, BUF_SIZE)) == 0)
     { 
         printf("nothing is write");    
     }
     else if((ret_write = write (BATT_fd, &buffer, BUF_SIZE)) == -1)
     { 
         printf("write error"); 
     }
     else
     {
         printf("wrote %d characters to file\n", ret_write);
         printf("address writeen is %x\n", buffer[i]);
     }

     if((ret_read = read(BATT_fd, &buffer, BUF_SIZE)) > 0)
     { 
        perror("read"); 
        return 4;
     }
     else
     {
        while((ret_read = read (BATT_fd, &buffer, BUF_SIZE)) > 0)
        {
            fwrite(buffer, 1, ret_read, stdout);
        }
     }

 close (BATT_fd);

 return 0;
}

output:

Answer 1

Before reading data from file, you need to move current position in file to the begining. That's because your write operations have moved current position to the end of file, so there is nothing left for reading ;).

see fseek

EDIT:

lseek would be better in your case (see comments)