copying binary file

Hi everybody,

I am new in C I have learned it just couple of months ago, I wrote program that reads a file and it must copy it to another file in binary mode, also I must use fseek(),ftel() and for loop in this assignment but I don’t know why the program is not working as expected. I appreciate if any body can help.

Code:

#include <stdio.h>

#define BUFLEN 1024

int main()
{
	FILE *in;
	FILE *out;

    char buf[BUFLEN];
    char in_name[12];
    char out_name[12];

    long file_size;
    int i,num1,size_moved,length;
    int *data;



    printf("\nEnter the source file name: ");
    scanf("%s",&in_name);

    printf("\nEnter the destination file name: ");
    scanf("%s",&out_name);



	in = fopen(in_name,"rb");      /* open source file */

	if (in == NULL)
	{
		puts("\nUnable to open the source file.");
		return(0);
	}

	out = fopen(out_name,"wb");  /* open destination file */

	if (out == NULL)
	{
		puts("\nUnable to create the destination file.");
		return(0);
	}

    fseek(in, -1L, SEEK_END);    /* move to the end of source file */

    file_size = ftell(in);       /* get file size */

    fseek(in, 0L, SEEK_SET);     /* move to the top of source file */

    if (file_size <= BUFLEN)     /* if source file size is 1024 byte */
    {                            /* long or less write to destination file */
       length = file_size;       /* in one time. */

       fread(&data, length, 1, in);

       fwrite(&data, length, 1, out);
    }
    else                         /* if source file size greater than 1024 byte */
    {                            /* write destination file many times using    */
        num1 = file_size / BUFLEN;  /* for loop */

        for (i=1;i<=num1;i++)
        {
           fread(&data, BUFLEN, 1, in);

           fwrite(&data, BUFLEN, 1, out);
        }

        size_moved = BUFLEN * num1;       /* calculate remaining of the file  */
                                          /* and write it to destination file */
        length = file_size - size_moved;

        fread(&data, length, 1, in);

        fwrite(&data, length, 1, out);

     }

    /* Close the files */

	fclose(in);
	fclose(out);

	return(0);
}

A few pointers:

>>scanf("%s",&in_name);
You don't need the &. Make it:
>>scanf("%s",in_name);
or better still, use fgets(), like in here:
http://faq.cprogramming.com/cgi-bin/...&id=1043284385

>>scanf("%s",&out_name);
Same thing

>>fread(&data, length, 1, in);
The data variable is a pointer, so you don't need the &. But then data isn't pointing to valid memory, so your use is way wrong. Maybe you meant to use the buf variable instead?

Why are you using fseek()/ftell() etc? It's unnecessary. Just read and write until you hit end of file. Something like:

Code:

while ((nbytes = fread(buf, 1, sizeof(buf), in)) > 0)
{
  fwrite (buf, 1, nbytes, out);
}

Thank you Hammer for your reply, but is it possible to use For loop instead of While loop.

it would be kindof pointless but it could be written as

Code:

for( ;(nbytes=fread(buf,1,sizeof(buf),in)>0; ){
        fwrite (buf,1,nbytes,out);
}

for loops are usually for programs that are going to loop either a constant number of times or a variable number of times. Use the while loop for function returns usually

It is always better to print the error messages to error output as in the code below,

Code:

if( in == NULL)
{
      fprintf(stderr,"\nUnable to open the source file.");
      return 1;
}

Whenever a program terminates abnormally due to some error, its exit code has to be non - zero (it is just a convention) i.e., 1 in the above code. So for each error quit in the program, different exit codes can be used. Exit code of 0 indicates successful execution of the program.

Thanks for all comments the program is working now.