std::basic_istream::readsome(3)

NAME
std::basic_istream::readsome - std::basic_istream::readsome

Synopsis
   std::streamsize readsome( char_type* s, std::streamsize count );
   Extracts up to count immediately available characters from the input stream. The
   extracted characters are stored into the character array pointed to by s.
   Behaves as UnformattedInputFunction. After constructing and checking the sentry
   object,
     * If rdbuf()->in_avail() == -1, calls setstate(eofbit) and extracts no characters.
     * If rdbuf()->in_avail() == 0, extracts no characters.
     * If rdbuf()->in_avail() > 0, extracts std::min(rdbuf()->in_avail(), count)
       characters and stores them into successive locations of the character array
       whose first element is pointed to by s.

Parameters
   s - pointer to the character array to store the characters to
   count - maximum number of characters to read

Return value
   The number of characters actually extracted.

Exceptions
   failure if an error occurred (the error state flag is not goodbit) and exceptions()
   is set to throw for that state.
   If an internal operation throws an exception, it is caught and badbit is set. If
   exceptions() is set for badbit, the exception is rethrown.

Notes
   The behavior of this function is highly implementation-specific. For example, when
   used with std::ifstream, some library implementations fill the underlying filebuf
   with data as soon as the file is opened (and readsome() on such implementations
   reads data, potentially, but not necessarily, the entire file), while other
   implementations only read from file when an actual input operation is requested (and
   readsome() issued after file opening never extracts any characters). Likewise, a
   call to std::cin.readsome() may return all pending unprocessed console input, or may
   always return zero and extract no characters.

Example
// Run this code
 #include <iostream>
 #include <sstream>
 int main()
 {
     char c[10] = {};
     std::istringstream input("This is sample text."); // std::stringbuf makes its entire
                        // buffer available for
                        // unblocking read
     input.readsome(c, 5); // reads 'This ' and stores in c[0] .. c[4]
     input.readsome(c, 9); // reads 'is sample' and stores in c[0] .. c[8]
     std::cout << c << '\n';
 }

Output:
 is sample

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