TRUNCATE(2) Linux Programmer's Manual TRUNCATE(2)
NAME
truncate, ftruncate - truncate a file to a specified length
SYNOPSIS
#include <unistd.h>
#include <sys/types.h>
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
truncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
ftruncate():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.3.5: */ _POSIX_C_SOURCE >= 200112L
DESCRIPTION
The truncate() and ftruncate() functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely
length bytes.
If the file previously was larger than this size, the extra data is lost. If the file previously was shorter, it is extended, and the
extended part reads as null bytes ('