Thread: Swapping byte order, aka Big endian?

What's wrong with ntohl?

Which header would I have to include for that? Sorry if it's obvious.

EDIT
I suppose it would help to know that I'm on windows.

Oh, looks like I had forgotten to add -lws2_32 to my linker. I managed to get Winsock.h to work, and ntohl did the trick. Thanks very much for the help.

When in doubt, consult the documentation:

ntohl Function (Windows)

Careful with ntohl(). First off, as you note, it's not portable (it exists on unix systems, but of course not in winsock2.h). Second, it won't do any swapping if the native system is big endian: it converts network byte-order (big endian) to host byte-order (which could also be big endian).

If you want to swap a four-byte integer in all cases, just write your own swap function; it's easy enough to do. If you do only want to swap if the native system is little endian, ntohl() is probably the best method, but you'll have to deal with the whole portability issue.

Here is something that should be portable:

Code:

        unsigned long int m, n;

        ...

        m =  (n & 0xff000000) >> 24;
        m |= (n & 0x00ff0000) >> 8;
        m |= (n & 0x0000ff00) << 8;
        m |= (n & 0x000000ff) << 24;