How to make a pointer increment by 1 byte, not 1 unit

Question

I have a structure tcp_option_t, which is N bytes. If I have a pointer tcp_option_t* opt, and I want it to be incremented by 1, I can't use opt++ or ++opt as this will increment by sizeof(tcp_option_t), which is N.

I want to move this pointer by 1 byte only. My current solution is

opt = (tcp_option_t *)((char*)opt+1);

but it is a bit troublesome. Are there any better ways?

Amity

That's probably the only solution. – Seely

You really don't want to do that...or, perhaps, why on earth do you think you want to do that (because you really don't want to do that!)? – Snowfield

No, that's exactly the right way to do it. But why would you want to? – Wayless

Answer 1

I'd suggest you to create a pointer of char and use it to transverse your struct.

char *ptr = (char*) opt;
++ptr; // will increment by one byte

when you need to restore your struct again, from ptr, just do the usual cast:

opt = (tcp_option_t *) ptr;

Elbertelberta

That won't work at all if ptr has been incremented by less than sizeof tcp_option_t . – Menagerie

Answer 2

I know this post is very old, but I had the same question and found this solution:

char **ptr = (char**) &opt;
++(*ptr); // will increment opt by one byte

No need to restore the struct.

This is working on Visual Studio 2005. I hope it works with all compiler.

Metaphysics

Sorry, but what does this answer add to the already given one (except unnecessary asterisks and confusion?) – Pantelleria