std::streamsize(3)

NAME
std::streamsize - std::streamsize

Synopsis
   Defined in header <ios>
   typedef /*implementation-defined*/ streamsize;
   The type std::streamsize is an implementation-defined signed integral type used to
   represent the number of characters transferred in an I/O operation or the size of an
   I/O buffer. It is used as a signed counterpart of std::size_t, similar to the POSIX
   type ssize_t.
   Except in the constructors of std::strstreambuf, negative values of std::streamsize
   are never used.

See also
   gcount returns number of characters extracted by last unformatted input operation
          (public member function of std::basic_istream<CharT,Traits>)
   ignore extracts and discards characters until the given character is found
          (public member function of std::basic_istream<CharT,Traits>)
   read extracts blocks of characters
          (public member function of std::basic_istream<CharT,Traits>)
   write inserts blocks of characters
          (public member function of std::basic_ostream<CharT,Traits>)