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NetBSD 6.1.5 - man page for ftruncate (netbsd section 2)

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

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

     Standard C Library (libc, -lc)

     #include <unistd.h>

     truncate(const char *path, off_t length);

     ftruncate(int fd, off_t length);

     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.

     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.

     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 writ-


     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).

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

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

BSD					  March 16, 2008				      BSD
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