Returns the number of characters available in the get area. If a read position is available, effectively returns egptr() - gptr(), 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
 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 -1 if no characters are available in the associated sequence as far as showmanyc() can tell.
|This section is incomplete
Reason: no example
 See also
| optionally provides the number of characters available for input from the file
(virtual protected member function of
| extracts already available blocks of characters
(public member function of