virtual std::streamsize showmanyc()

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



Return value

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


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"


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

#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

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

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