_IONBF macro — No buffering
const int _IONBF
When passed as the mode
parameter to setvbuf
, the
_IONBF
macro disables the
buffering of an open file. Characters are read or written as soon as
possible, without buffering. The _IONBF
macro expands to a constant
integer.
Support for unbuffered streams is implementation-dependent. For example, a host operating system might line buffer input from a terminal, even if a program requests unbuffered input.