reinterpret_cast double to char*

Question

How can I reinterpret cast from double to char* (I need it to store the data of double in file in bytes). Below is the code and I don't know why it doesn't work:

#include <iostream>
int main(int argc, char **argv)
{
    const double tmpDouble = 1234.;
    char *tmpChar = reinterpret_cast<char*>(tmpDouble);
    return 0;
}

Answer 1

If what you had there worked, it probably wouldn't be what you want - the pointer's value would just be 1234 - effectively pointing to that address which might contain anything (not that it's accessible).

If you just want to have the double in binary format, you could do

const byte* pDouble = reinterpret_cast<const byte*>(&tmpDouble);
//                                      |
//                             note the address here

But first check whatever it is you're using to write to file for a function prototype that takes a double directly.