netbsd man page for ftruncate

TRUNCATE(2)						      BSD System Calls Manual						       TRUNCATE(2)

NAME
     truncate, ftruncate -- truncate a file to a specified length

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     truncate(const char *path, off_t length);

     int
     ftruncate(int fd, off_t length);

DESCRIPTION
     truncate() causes the file named by path or referenced by fd to have a size of length bytes.  If the file previously was larger than this
     size, the extra data is discarded.  If it was previously shorter than length, its size is increased to the specified value and the extended
     area appears as if it were zero-filled.

     With ftruncate(), the file must be open for writing; for truncate(), the process must have write permissions for the file.

RETURN VALUES
     A value of 0 is returned if the call succeeds.  If the call fails a -1 is returned, and the global variable errno specifies the error.

ERRORS
     Error return codes common to truncate() and ftruncate() are:

     [EISDIR]		The named file is a directory.

     [EROFS]		The named file resides on a read-only file system.

     [ETXTBSY]		The file is a pure procedure (shared text) file that is being executed.

     [EIO]		An I/O error occurred updating the inode.

     [ENOSPC]		There was no space in the filesystem to complete the operation.

     Error codes specific to truncate() are:

     [ENOTDIR]		A component of the path prefix is not a directory.

     [ENAMETOOLONG]	A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} characters.

     [ENOENT]		The named file does not exist.

     [EACCES]		Search permission is denied for a component of the path prefix, or the named file is not writable by the user.

     [ELOOP]		Too many symbolic links were encountered in translating the pathname.

     [EFAULT]		path points outside the process's allocated address space.

     Error codes specific to ftruncate() are:

     [EBADF]		The fd is not a valid descriptor.

     [EINVAL]		The fd references a socket, not a file, or the fd is not open for writing.

SEE ALSO
     open(2)

STANDARDS
     Use of truncate() to extend a file is an IEEE Std 1003.1-2004 (``POSIX.1'') extension, and is thus not portable.  Files can be extended in a
     portable way seeking (using lseek(2)) to the required size and writing a single character with write(2).

HISTORY
     The truncate() and ftruncate() function calls appeared in 4.2BSD.

BUGS
     These calls should be generalized to allow ranges of bytes in a file to be discarded.

BSD
								  March 16, 2008							       BSD