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ftruncate(2) [bsd man page]

TRUNCATE(2)							System Calls Manual						       TRUNCATE(2)

NAME
truncate - truncate a file to a specified length SYNOPSIS
truncate(path, length) char *path; off_t length; ftruncate(fd, length) int fd; off_t length; DESCRIPTION
Truncate causes the file named by path or referenced by fd to be truncated to at most length bytes in size. If the file previously was larger than this size, the extra data is lost. 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. [EINVAL] The pathname contains a character with the high-order bit set. [ENAMETOOLONG] A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. [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 translating 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. 4.2 Berkeley Distribution March 29, 1986 TRUNCATE(2)

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

NAME
ftruncate, truncate -- truncate or extend a file to a specified length SYNOPSIS
#include <unistd.h> int ftruncate(int fildes, off_t length); int truncate(const char *path, off_t length); DESCRIPTION
ftruncate() and truncate() cause the file named by path, or referenced by fildes, to be truncated (or extended) to length bytes in size. If the file size exceeds length, any extra data is discarded. If the file size is smaller than length, the file is extended and filled with zeros to the indicated length. The ftruncate() form requires the file to be open for writing. Note: ftruncate() and truncate() do not modify the current file offset for any open file descriptions associated with 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
The ftruncate() system call will fail if: [EBADF] fildes is not a valid descriptor open for writing. [EFBIG] The file is a regular file and length is greater than the offset maximum established in the open file description associ- ated with fildes. [EINVAL] fildes references a socket, not a file. [EINVAL] fildes is not open for writing. [EROFS] The named file resides on a read-only file system. The truncate() system call will fail if: [EACCES] Search permission is denied for a component of the path prefix. [EACCES] The named file is not writable by the user. [EFAULT] Path points outside the process's allocated address space. [EISDIR] The named file is a directory. [ELOOP] Too many symbolic links are encountered in translating the pathname. This is taken to be indicative of a looping symbolic link. [ENAMETOOLONG] A component of a pathname exceeds {NAME_MAX} characters, or an entire path name exceeds {PATH_MAX} characters. [ENOENT] The named file does not exist. [ENOTDIR] A component of the path prefix is not 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. The ftruncate() and truncate() system calls will fail if: [EFBIG] The length argument was greater than the maximum file size. [EINTR] A signal is caught during execution. [EINVAL] The length argument is less than 0. [EIO] An I/O error occurred while reading from or writing to a file system. 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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