Low-level I/O

These functions invoke the operating system directly for lower-level operation than that provided by stream I/O. Low-level input and output calls don't buffer or format data.

Low-level routines can access the standard streams opened at program startup using the following predefined file descriptors.

Stream	File Descriptor
stdin	0
stdout	1
stderr	2

Low-level I/O routines set the errno global variable when an error occurs. You must include STDIO.H when you use low-level functions only if your program requires a constant that is defined in STDIO.H, such as the end-of-file indicator (EOF).

Low-level I/O functions

Function	Use
_close	Close file
_commit	Flush file to disk
_creat, _wcreat	Create file
_dup	Return next available file descriptor for given file
_dup2	Create second descriptor for given file
_eof	Test for end of file
_lseek, _lseeki64	Reposition file pointer to given location
_open, _wopen	Open file
_read	Read data from file
_sopen, _wsopen, _sopen_s, _wsopen_s	Open file for file sharing
_tell, _telli64	Get current file-pointer position
_umask, _umask_s	Set file-permission mask
_write	Write data to file

_dup and _dup2 are typically used to associate the predefined file descriptors with different files.

See also

Input and output
Universal C runtime routines by category
System calls