How to read registers: RAX, RBX, RCX, RDX, RSP. RBP, RSI, RDI in C or C++?

Lets say I want to read values from those registers (and pretty all thats it) on dual core x64 CPU. How can I do this? Can I simply write something like:

uint64_t rax = 0, rbx = 0;
__asm__ __volatile__ (
    /* read value from rbx into rbx */
    "movq %%rdx, %0;\n"
    /* read value from rax into rax*/
    "movq %%rax, %1;\n"
    /* output args */
    : "=r" (rbx), "=r" (rax)
    : /* no input */
    /* clear both rdx and rax */
    : "%rdx", "%rax"
);

and then just print out rax and rbx? Cheers