Load binary file using fstream

Question

I'm trying to load binary file using fstream in the following way:

#include <iostream>
#include <fstream>
#include <iterator>
#include <vector>

using namespace std;

int main()
{
    basic_fstream<uint32_t> file( "somefile.dat", ios::in|ios::binary );

    vector<uint32_t> buffer;
    buffer.assign( istream_iterator<uint32_t, uint32_t>( file ), istream_iterator<uint32_t, uint32_t>() );

    cout << buffer.size() << endl;

    return 0;
}

But it doesn't work. In Ubuntu it crashed with std::bad_cast exception. In MSVC++ 2008 it just prints 0.

I know that I could use file.read to load file, but I want to use iterator and operator>> to load parts of the file. Is that possible? Why the code above doesn't work?

Answer 1

1. istream_iterator wants basic_istream as argument.
2. It is impossible to overload operator>> inside basic_istream class.
3. Defining global operator>> will lead to compile time conflicts with class member operator>>.
4. You could specialize basic_istream for type uint32_t. But for specialization you should rewrite all fuctionons of basic_istream class. Instead you could define dummy class x and specialize basic_istream for it as in the following code:

using namespace std;

struct x {};
namespace std {
template<class traits>
class basic_istream<x, traits> : public basic_ifstream<uint32_t>
{
public:
    explicit basic_istream<x, traits>(const wchar_t* _Filename, 
        ios_base::openmode _Mode, 
        int _Prot = (int)ios_base::_Openprot) : basic_ifstream<uint32_t>( _Filename, _Mode, _Prot ) {}

    basic_istream<x, traits>& operator>>(uint32_t& data)
    {
        read(&data, 1);
        return *this;
    }
};
} // namespace std 

int main() 
{
    basic_istream<x> file( "somefile.dat", ios::in|ios::binary );
    vector<uint32_t> buffer;
    buffer.assign( istream_iterator<uint32_t, x>( file ), istream_iterator<uint32_t, x>() );
    cout << buffer.size() << endl;
    return 0;
}