< cpp‎ | io‎ | basic streambuf
virtual std::streamsize showmanyc();

Estimates the number of characters available for input in the associated character sequence. underflow() is guaranteed not to return Traits::eof() or throw an exception until at least that many characters are extracted.


[edit] Parameters


[edit] Return value

The number of characters that are certainly available in the associated character sequence, or -1 if showmanyc can determine, without blocking, that no characters are available. If showmanyc returns -1, underflow() and uflow() will definitely return Traits::eof or throw.

The base class version returns 0, which has the meaning of "unsure if there are characters available in the associated sequence".

[edit] Notes

The name of this function stands for "stream: how many characters?", so it is pronounced "S how many C", rather than "show many C".

[edit] Example

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 159 C++98 underflow() is guaranteed not to fail until
at least showmanyc() characters are supplied
extended the guarantee to allow at least
showmanyc() characters to be extracted

[edit] See also

obtains the number of characters immediately available in the get area
(public member function) [edit]
optionally provides the number of characters available for input from the file
(virtual protected member function of std::basic_filebuf<CharT,Traits>) [edit]