cpp/io/basic streambuf/in avail

Returns the number of characters available in the get area. If a read position is available, effectively returns, the size of the get area. In this case, the number of bytes returned is the number of bytes that can be extracted from the buffer without calling underflow.

If the get area is empty, calls showmanyc to determine the number of bytes available in the associated character sequence. In this case, the value returned is the number of bytes that can be extracted from the buffer while it's guaranteed that underflow would not return.

Parameters
(none)

Return value
The number of characters available for non-blocking read (either the size of the get area or the number of characters ready for reading from the associated character sequence), or if no characters are available in the associated sequence as far as showmanyc can tell.