One 32bit Long into 4 8bit Chars

In C code

I'm gonna ask a stupid question here, but I'm not sure I trust my code so I want to hear if you can tell me what's wrong with my approach

Right now, the code goes

long data

char data0
char data1
char data2
char data3

data0 = data;
data1 = data >> 8;
data2 = data >> 16;
data3 = data >> 24;

but I'm not sure that's the best approach, or even a good approach. It works, which is most important obviously, but I have this nagging feeling that there's something very not Best Practices about this approach and I can't shake that feeling.

My problem is, when I do

char a;
long b;
a=b;

how can I be sure that a is filled with the eight rightmost bits, rather than the eight leftmost?