How do I send floats in window messages.

Answer 1

You could use memcpy:

#include <memory.h>
int main() {
    float f = 1.0;
    int n;
    memcpy( &n, &f, sizeof(f) );
}

I don't think there is an elegant solution to this, but whatever you do, I'd wrap it in a function to make it obvious what I was up to:

int FloatToInt( float f ) {
    int n;
    assert( sizeof(n) == sizeof(f) );
    memcpy( &n, &f, sizeof(f) );
    return n;
}

Answer 2

I would prefer the union. It is the clearest and easiest to understand. It also probably has the least amount of undefined behavior.

Answer 3

Use reinterpret_cast< WPARAM &>(f). This cast is not restricted to pointers, it also works with references.

Answer 4

I'd go the simple way of taking a pointer to your float, casting it to a pointer to UINT, and then dereferencing the resulting pointer:

WPARAM wParam = *((UINT*)(&f));

To convert it back you do the opposite. Doing the cast at pointer-level makes sure the compiler won't try any "conversion" behind your back.

float f = *((float*)(&wParam))