ftruncate man page on OpenDarwin

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

NAME
     truncate, ftruncate — truncate or extend a file to a specified length

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 be trun‐
     cated or extended to length bytes in size.	 If the file previously was
     larger than this size, the extra data is lost. If the file was smaller
     than this size, it will be extended as if by writing bytes with the value
     zero.  With ftruncate(), the file must be open for writing.

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
     Truncate() succeeds unless:

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

     [ENAMETOOLONG]	A component of a pathname exceeded {NAME_MAX} charac‐
			ters, or an entire path name exceeded {PATH_MAX} char‐
			acters.

     [ENOENT]		The named file does not exist.

     [EACCES]		Search permission is denied for a component of the
			path prefix.

     [EACCES]		The named file is not writable by the user.

     [ELOOP]		Too many symbolic links were encountered in translat‐
			ing the pathname.

     [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.

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

     Ftruncate() succeeds unless:

     [EBADF]		The fd is not a valid descriptor.

     [EINVAL]		The fd references a socket, not a file.

     [EINVAL]		The fd is not open for writing.

SEE ALSO
     open(2)

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

     Use of truncate() to extend a file is not portable.

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

4.2 Berkeley Distribution	 June 4, 1993	     4.2 Berkeley Distribution
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