std::basic_ifstream::rdbuf

// read file data using associated buffer's members
#include <iostream>     // std::cout
#include <fstream>      // std::filebuf, std::ifstream
int main () {
  std::ifstream ifs ("test.txt", std::ifstream::binary);
  // get pointer to associated buffer object
  std::filebuf* pbuf = ifs.rdbuf();
  // get file size using buffer's members
  std::size_t size = pbuf->pubseekoff (0,ifs.end,ifs.in);
  pbuf->pubseekpos (0,ifs.in);
  // allocate memory to contain file data
  char* buffer=new char[size];
  // get file data
  pbuf->sgetn (buffer,size);
  ifs.close();
  // write content to stdout
  std::cout.write (buffer,size);
  delete[] buffer;
  return 0;
}