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

 

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Symbols index

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Input/output library

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C-style I/O

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basic_streambuf

basic_filebuf

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basic_spanbuf (C++23)

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basic_osyncstream (C++20)

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std::basic_filebuf

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basic_filebuf::basic_filebuf

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basic_filebuf::operator= (C++11)

basic_filebuf::swap (C++11)

basic_filebuf::is_open

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Protected member functions

basic_filebuf::showmanyc

basic_filebuf::underflow

basic_filebuf::uflow

basic_filebuf::pbackfail

basic_filebuf::overflow

basic_filebuf::setbuf

basic_filebuf::seekoff

basic_filebuf::seekpos

basic_filebuf::sync

basic_filebuf::imbue

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swap(std::basic_filebuf) (C++11)

 

protected: virtual std::streamsize showmanyc()

If implemented, returns the number of characters left to read from the file.

Parameters

(none)

Return value

The number of characters available for reading from the file, or -1 if the end of file was reached.

Notes

This function is optional. If not implemented, this function returns ​0​ (since the base class version std::basic_streambuf::showmanyc gets called)

Whether implemented or not, this function is normally called by std::basic_streambuf::in_avail if the get area is empty.

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

Example

implementation test to see if showmanyc() is implemented for filebuf

Run this code

#include <fstream>
#include <iostream>
 
struct mybuf : std::filebuf
{
     using std::filebuf::showmanyc;
};
 
int main()
{
    mybuf fin;
    fin.open("main.cpp", std::ios_base::in);
    std::cout << "showmanyc() returns " << fin.showmanyc() << '\n';
}

Possible output:

showmanyc() returns 267

See also

in_avail	obtains the number of characters immediately available in the get area (public member function of std::basic_streambuf<CharT,Traits>)
readsome	extracts already available blocks of characters (public member function of std::basic_istream<CharT,Traits>)