C++ read the whole file in buffer

There's no need for wrapper classes for very basic functionality:

std::ifstream file("myfile", std::ios::binary | std::ios::ate);
std::streamsize size = file.tellg();
file.seekg(0, std::ios::beg);

std::vector<char> buffer(size);
if (file.read(buffer.data(), size))
{
    /* worked! */
}

You can access the contents of a file with a input file stream std::ifstream, then you can use std::istreambuf_iterator to iterate over the contents of the ifstream,

std::string
getFileContent(const std::string& path)
{
  std::ifstream file(path);
  std::string content((std::istreambuf_iterator<char>(file)), std::istreambuf_iterator<char>());

  return content;
}

In this case im using the iterator to build a new string using the contents of the ifstream, the std::istreambuf_iterator<char>(file) creates an iterator to the begining of the ifstream, and std::istreambuf_iterator<char>() is a default-constructed iterator that indicate the special state "end-of-stream" which you will get when the first iterator reach the end of the contents.