Question

I have problem converting String^ containing 8 bytes as characters (as ascii) to double.
I want to take those 8 characters and convert them binary to double.

What would you recommend to do this conversion in C++/cli?

I was trying to use Marshal::Copy, Double::TryParse, etc.

Maybe I use wrong specifications of parameters, but I really lost my last hopes.
There must be something easy to do this conversion.

Thanks.

Answer 1

Well, the bad news is that the System.String class uses only Unicode encoding internally.

So if you give it bytes it will map them to its internal encoding hiding the original value.

The good news is that you can play with the System.Text.Encoding class to retrieve 8bits values corresponding to the unicode characters.

Here is a sample :

#include <iostream>

using namespace System;
using namespace System::Text;

int main()
{
    int n = 123456;
    double d = 123.456;

    std::cout << n << std::endl;
    std::cout << d << std::endl;

    char* n_as_bytes = (char*)&n;
    char* d_as_bytes = (char*)&d;

    String^ n_as_string = gcnew String(n_as_bytes, 0, sizeof(n));
    String^ d_as_string = gcnew String(d_as_bytes, 0, sizeof(d));

    Encoding^ ascii = Encoding::GetEncoding("iso-8859-1");

    array<Byte>^ n_as_array = ascii->GetBytes(n_as_string);
    array<Byte>^ d_as_array = ascii->GetBytes(d_as_string);

    cli::pin_ptr<unsigned char> pin_ptr_n = &n_as_array[0];
    cli::pin_ptr<unsigned char> pin_ptr_d = &d_as_array[0];

    unsigned char* ptr_n = pin_ptr_n;
    unsigned char* ptr_d = pin_ptr_d;

    int n_out = *(int*)ptr_n;
    double d_out = *(double*)ptr_d;

    std::cout << n_out << std::endl;
    std::cout << d_out << std::endl;

    return 0;
}

This should give you :

123456
123.456
123456
123.456

Not sure it is completely safe, but trying it in your context should be a good start to ensure it is viable. 🙂