| Standards / Extensions | C or C++ | Dependencies |
|---|---|---|
XPG4.2 |
both |
#define _XOPEN_SOURCE_EXTENDED 1
#include <unistd.h>
int truncate(const char *path, off_t length);Truncates the file indicated by the path to the indicated length. The calling process must have write permission for the file. If the file size exceeds length, any extra data is discarded. If the file size is smaller than length, bytes between the old and new lengths are read as zeros. A change to the size of the file has no impact on the file offset.
If truncate() would cause the file size to exceed the soft file size limit for the process, truncate() will fail and a SIGXFSZ signal will be generated for the process.
If successful, truncate() marks the st_ctime and st_mtime fields of the file.
If unsuccessful, the file is unchanged.
Large file support for z/OS UNIX files: Large z/OS UNIX files are supported automatically for AMODE 64 C/C++ applications. AMODE 31 C/C++ applications must be compiled with the option LANGLVL(LONGLONG) and define the _LARGE_FILES feature test macro before any headers are included to enable this function to operate on z/OS UNIX files that are larger than 2 GB in size. File size and offset fields are enlarged to 63 bits in width. Therefore, any other function operating on the file is required to define the _LARGE_FILES feature test macro as well.
If successful, truncate() returns 0.