ftruncate

ftruncate

Truncate a File

Portability: POSIX.1 conforming

SYNOPSIS
DESCRIPTION
RETURN VALUE
IMPLEMENTATION
EXAMPLE
SEE ALSO

SYNOPSIS

#include <unistd.h>

int ftruncate(int fn, off_t length);

DESCRIPTION

ftruncate truncates an USS file open for write access to length in bytes. fn is the file descriptor for the file to be truncated. ftruncate does not change the current file position.

RETURN VALUE

ftruncate returns a 0 if it is successful and a -1 if it is not successful.

IMPLEMENTATION

Data beyond the end of the truncated file are lost. If the file size is smaller than the specified length , the file is unchanged.

EXAMPLE

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

main()
{
   FILE *testfile;
   int fd, long size;
   char flname[] ="trunc.test";

   if ((fd=creat(flname,S_IRUSR1)) < 0)
      perror("creat() error");
   else {
      if ((testfile = fdopen(fd, "w")) == NULL) {
         perror("fdopen() error");
         close(fd);
      }
   }
   fputs("ABCDEFGHIJKLMNOPQRSTUVWXYZ",testfile);
   fflush(testfile);
   size = lseek(fd, 0, SEEK_END);
   printf("The file is %ld bytes long.\n", size);

   if (ftruncate(fd, 3) !=0)
      perror("ftruncate() error");
   else {
      size = lseek(fd, 0, SEEK_END);
      printf("The file is now %ld bytes long.\n", size);
   }
fclose(testfile);
unlink(flname);
}