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

 

C++

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

 

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)

 

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

 

protected: virtualstd::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.

Parameters

(none)

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".

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".

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

See also

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