Question

I can’t compile this, how should I move [eax+4] to y in Visual Studio?

float x, y, z;

__asm
{
    mov x,      eax
    mov y,      [eax+4]
    mov z,      [eax+8]
}

EDIT:

Error 1 error C2424: ‘+’ : improper expression in ‘second operand’

Answer 1

You’re using eax as a pointer, so storing that bit-pattern into float x seems unlikely. Perhaps you meant to copy 3 floats from memory at [eax+0], +4, and +8?

@RaymondChen is right, you can use a temporary register to transfer it. The obvious choice is to pick ECX or EDX as a temporary; those along with EAX are call-clobbered so using them won’t force the compiler to save/restore them in the function containing your asm block.

Even though the values are float, you can copy them with 32-bit integer registers instead of through XMM0 or an x87 register; you’re not doing FP math on them.

mov   ecx, [eax]
mov   x, ecx            // you probably want this, not  mov x, eax
mov   ecx, [eax+4]
mov   y, ecx
mov   ecx, [eax+8]
mov   z, ecx

If you knew x and y were contiguous, you could copy 8 bytes at once with an XMM register.