cpp/io/basic streambuf/underflow

Ensures that at least one character is available in the input area by updating the pointers to the input area (if needed) and reading more data in from the input sequence (if applicable). Returns the value of that character (converted to with ) on success or  on failure.

The function may update, and  pointers to define the location of newly loaded data (if any). On failure, the function ensures that either or.

The base class version of the function does nothing. The derived classes may override this function to allow updates to the get area in the case of exhaustion.

Parameters
(none)

Return value
The value of the character pointed to by the get pointer after the call on success, or otherwise.

The base class version of the function returns.

Note
The public functions of std call this function only if or.