open/4 option: overflow(OverFlowAction) QP_stream: unsigned char overflow
Written characters are stored in the buffer of an output stream by the
middle layer output function until the
current record is terminated, through a newline operation (such as
by writing the line border code of the stream.
If a character is written when the buffer of an output stream is full,
it overflows the output buffer.
overflow field specifies
the action that the middle layer function should take if this happens.
The possible values for
open/4. It is an error when output stream buffer overflows.
open/4. Keeps the characters in the buffer and throws away the current character that overflows the output buffer.
open/4. Pass the current buffer storing a partial record of the output stream to the bottom layer flush function to write out the buffer. The host operating system must support writing of partial records for the device associated with the stream.
Note that if an output stream is unbuffered (i.e.
max_reclen is 0)
then the middle layer function ignores the
overflow field and
write function for each character written to the stream.