std::basic_istream::gcount(3)

NAME
std::basic_istream::gcount - std::basic_istream::gcount

Synopsis
   std::streamsize gcount() const;
   Returns the number of characters extracted by the last unformatted input operation,
   or the maximum representable value of std::streamsize if the number is not
   representable.
   The following member functions of basic_istream change the value of subsequent
   gcount() calls:
     * move constructor
     * swap()
     * get()
     * getline()
     * ignore()
     * read()
     * readsome()
     * operator>>(basic_streambuf*)
   The following functions set gcount() to zero:
     * constructor
     * putback()
     * unget()
     * peek()

Parameters
   (none)

Return value
   The number of characters extracted by the last unformatted input operation, or the
   maximum representable value of std::streamsize if the number is not representable.

Example
// Run this code
 #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
   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 3464 C++98 the return value was unspecified when the returns the maximum
                       result overflows value