std::basic_istream<CharT,Traits>::gcount
| std::streamsize gcount() const; | 
Returns the number of characters extracted by the last unformatted input operation.
The following member functions of basic_istream change the value of subsequent gcount() calls:
The following functions set gcount() to zero:
Parameters
(none).
Return value
The number of characters extracted by the last unformatted input operation.
Example
#include <iostream>
#include <sstream>
 
int main()
{
    char x[20];
    std::istringstream stream("Hello World");
 
    stream.read(x, sizeof x);
    std::cout << "Characters extracted: " << stream.gcount();
}Output:
Characters extracted: 11
    © cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
    http://en.cppreference.com/w/cpp/io/basic_istream/gcount