Copying one file to another

[countdrak]

I am doing this just as an exercise coz I ran into this problem in something I was doing.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
	FILE *from, *to;
	char file1[100], file2[100], buffer[8192];


	printf("Name of file to be copied: ");
	gets(file1);
	printf("\nName of file to be copied to: ");
	gets(file2);

	from = fopen(file1, "r");
	to = fopen(file2, "w");


	while (!feof(from))
	{
		fread(buffer, sizeof(char), 8192, from);
		fwrite(buffer, sizeof(char), 8192, to);
	}

	fclose(from);
	fclose(to);
	return 0;
}

Now this might look simple enough, but its not, coz im trying to copy a 600MB file bit by bit, but it only makes a 4kb or 5kb or 9kb file depending on the buffer size I give.

Why is this happening? And how to correct it?

 

[countdrak]

Ok I guess you can write something like this.

#include <stdio.h>
#include <stdlib.h>

int main () {
  FILE * pFile, *wFile;
  long lSize;
  char * buffer;

  pFile = fopen ( "023LW.rf" , "rb" );
  wFile = fopen ( "copied.txt", "w");
  if (pFile==NULL) exit (1);

  // obtain file size.
  fseek (pFile , 0 , SEEK_END);
  lSize = ftell (pFile);
  rewind (pFile);

  // allocate memory to contain the whole file.
  buffer = (char*) malloc (lSize);
  if (buffer == NULL) exit (2);

  // copy the file into the buffer.
  fread (buffer,1,lSize,pFile);
  fwrite(buffer, 1, lSize, wFile);

  /*** the whole file is loaded in the buffer. ***/

  // terminate
  fclose (pFile);
  fclose (wFile);
  free (buffer);
  return 0;
}

But I want to pick up a chunk of values, process, dump them and repeat the process again until the end of file. But it seems !feof(FILE *) does not work as it ends the file early.

Why oh why!

 

[countdrak]

Ha ha ha! Sorry everyone...had to open the file in "rb" mode. Everything is working now.

Great!

 

[sedj]

Bear in mind that in your second example, you are in effect malloc'ing a serious amount of memory (you mention 600 MB files) - and you run the risk of hogging system resources, and going into swap.

Much better IMO to read and write the files in chunks, and ease up on the RAM

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[ArkM]

Some additions:
1. Open target file in "wb" mode.
2. Test if a target file was opened (need permissions to open an existent file for rewriting). Check fread() result too (i/o errors?).
3. See sedj's remark: it's a serious problem.
4. Press <Ctrl-Z> <Enter> instead of file name or type a long (long file name... Avoid gets where possible (always use fgets.

 

[Salem]

> while (!feof(from))
Tell me, is your output file bigger than your input file?

Try this

size_t n;
while ( (n=fread(buffer, sizeof(char), sizeof(buffer), from)) != 0 ) {
  if ( fwrite(buffer, sizeof(char), n, to) != n ) {
    /* failed to write - disk full? */
  }
}

> gets(file1);
Oh the humanity!!!
Use fgets() and be safe.

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