std::basic_streambuf<CharT,Traits>::showmanyc

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

Input/output library

I/O manipulators
Print functions(C++23)
C-style I/O
Buffers
basic_streambuf
basic_filebuf
basic_stringbuf
basic_spanbuf (C++23)
strstreambuf (C++98/26*)
basic_syncbuf (C++20)
Streams
Abstractions
ios_base
basic_ios
basic_istream
basic_ostream
basic_iostream
File I/O
basic_ifstream
basic_ofstream
basic_fstream
String I/O
basic_istringstream
basic_ostringstream
basic_stringstream
Array I/O
basic_ispanstream (C++23)
basic_ospanstream (C++23)
basic_spanstream (C++23)
istrstream (C++98/26*)
ostrstream (C++98/26*)
strstream (C++98/26*)
Synchronized Output
basic_osyncstream (C++20)
Types
streamoff
streamsize
fpos
Error category interface
iostream_category (C++11)
io_errc (C++11)

[edit]

std::basic_streambuf

Public member functions
basic_streambuf::~basic_streambuf
Locales
basic_streambuf::pubimbue
basic_streambuf::getloc
Positioning
basic_streambuf::pubsetbuf
basic_streambuf::pubseekoff
basic_streambuf::pubseekpos
basic_streambuf::pubsync
Get area
basic_streambuf::in_avail
basic_streambuf::snextc
basic_streambuf::sbumpc
basic_streambuf::sgetc
basic_streambuf::sgetn
Put area
basic_streambuf::sputc
basic_streambuf::sputn
Putback
basic_streambuf::sputbackc
basic_streambuf::sungetc

Protected member functions
basic_streambuf::basic_streambuf
basic_streambuf::operator= (C++11)
basic_streambuf::swap (C++11)
Locales
basic_streambuf::imbue
Positioning
basic_streambuf::setbuf
basic_streambuf::seekoff
basic_streambuf::seekpos
basic_streambuf::sync
Get area
basic_streambuf::showmanyc
basic_streambuf::underflow
basic_streambuf::uflow
basic_streambuf::xsgetn
basic_streambuf::ebackbasic_streambuf::gptrbasic_streambuf::egptr
basic_streambuf::gbump
basic_streambuf::setg
Put area
basic_streambuf::xsputn
basic_streambuf::overflow
basic_streambuf::pbasebasic_streambuf::pptrbasic_streambuf::epptr
basic_streambuf::pbump
basic_streambuf::setp
Putback
basic_streambuf::pbackfail

[edit]

protected: virtualstd::streamsize showmanyc();

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

[edit]Parameters

(none)

[edit]Return value

The number of characters that are certainly available in the associated character sequence, or-1 ifshowmanyc can determine, without blocking, that no characters are available. Ifshowmanyc returns-1,underflow() anduflow() will definitely returnTraits::eof or throw.

The base class version returns0, 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

This section is incomplete
Reason: no 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

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