Syntax

#include <io.h>
int _chsize(int handle, long size);

• chsize lengthens or cuts off the file associated with handle to the length specified by size. You must open the file in a mode that permits writing. _chsize adds null characters (\0) when it lengthens the file. When _chsize cuts off the file, it erases all data from the end of the shortened file to the end of the original file.

• chsize returns the value 0 if it successfully changes the file size. A return value of -1 shows an error; _chsize sets errno to one of the following values:

  Value

  Meaning
  EACCESS
  The specified file is locked against access.
  EBADF
  The file handle is not valid, or the file is not open for writing.
  ENOSPC
  There is no space left on the device.
  EOS2ERR
  The call to the operating system was not successful.

This example opens a file named sample.dat and returns the current length of that file. It then alters the size of sample.dat and returns the new length of that file.

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

int main(void)
{
   long length;
   int fh;

   printf("\nCreating sample.dat.\n");
   system("echo Sample Program > sample.dat");
   if (-1 == (fh = open("sample.dat", O_RDWR|O_APPEND))) {
      printf("Unable to open sample.dat.\n");
      return EXIT_FAILURE;
   }
   if (-1 == (length = filelength(fh))) {
      printf("Unable to determine length of sample.dat.\n");
      return EXIT_FAILURE;
   }
   printf("Current length of sample.dat is %d.\n", length);
   printf("Changing the length of sample.dat to 20.\n");
   if (-1 == (_chsize(fh, 20))) {
      perror("chsize failed");
      return EXIT_FAILURE;
   }
   if (-1 == (length = _filelength(fh))) {
      printf("Unable to determine length of sample.dat.\n");
      return EXIT_FAILURE;
   }
   printf("New length of sample.dat is %d.\n", length);
   close(fh);
   return 0;

   /****************************************************************************
      The output should be similar to :

       Creating sample.dat.
       Current length of sample.dat is 17.
       Changing the length of sample.dat to 20.
       New length of sample.dat is 20.
   ****************************************************************************/
}

• filelength
  
• lseek

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