Is #pragma once ok to use as a guard mechanism?

[ekhule]

Hello,

sometimes I see guard mechanisms in .h files like so:

#ifndef _CLASSNAME_H_
#define _CLASSNAME_H_

...

#endif //(_CLASSNAME_H_)

doesnt "#pragma once" do the exact same thing but in one line of code? Why would anyone use the first method instead of "#pragma once" ?

Thank you,
Ellay