将整个文件读入string中

size_t GetFileSize(FILE* file) {
  fseek(file, 0, SEEK_END);
  return static_cast<size_t>(ftell(file));
}

std::string ReadEntireFile(FILE* file) {
  const size_t file_size = GetFileSize(file);
  char* const buffer = new char[file_size];

  size_t bytes_last_read = 0;  // # of bytes read in the last fread()
  size_t bytes_read = 0;       // # of bytes read so far

  fseek(file, 0, SEEK_SET);

  // Keeps reading the file until we cannot read further or the
  // pre-determined file size is reached.
  do {
    bytes_last_read = fread(buffer+bytes_read, 1, file_size-bytes_read, file);
    bytes_read += bytes_last_read;
  } while (bytes_last_read > 0 && bytes_read < file_size);

  const std::string content(buffer, bytes_read);
  delete[] buffer;

  return content;
}