c++ doubt

[netrix]

Hello guys, I need to learn a few basics about C++ for friday... can anyone tell me what does this C++ macro accomplish: #define func(a, b) a ^= b ^= a ^= b?! thanks in advance!

[Templarian]

Without actually knowing C++,

^= is the XOR equals operator

[BradLee]

At a glance, it looks very similar to the XOR swap algorithm, which swaps the values of a and b.

[Jeff Wheeler]

Yeah, I agree. It looks like it would swap the values.

[Templarian]

At a glance, it looks very similar to the XOR swap algorithm, which swaps the values of a and b.
creepy thats like exactly what my brother said when he looked over it real fast. Then he tried to explain how it didn't use a temporary variable so I just posed that.

[hybrid101]

that is some nice code:lol:

[Al6200]

Wow, it actually swaps:

a = 1010
b = 1101

a ^= b

a = 0111
b = 1101

b ^= a

a = 0111
b = 1010

a ^= b

a = 1101
b = 1010

I guess if a can store the difference between a and b, then b xoring itself with a will perform the first swap. But b now has the second value, so a xoring with that yields b. Cool, I didn't know it was possible to swap like that.

[λ]

this is a bad idea..

http://c-faq.com/expr/xorswapexpr.html

[BradLee]

^ Besides not working for an arbitrary random compiler, using a swap variable is usually FASTER than doing an XOR swap.

It's because the compiler can optimize the swap variable code to work in parallel much better. http://en.wikipedia.org/wiki/XOR_swap_algorithm