Question 20.15c

comp.lang.c FAQ list · Question 20.15c

Q: How can I swap two values without using a temporary?

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A: The standard hoary old assembly language programmer's trick is:

a ^= b;
b ^= a;
a ^= b;

But this sort of code has little place in modern, HLL programming. Temporary variables are essentially free, and the idiomatic code using three assignments, namely

int t = a;
 a = b;
 b = t;

is not only clearer to the human reader, it is more likely to be recognized by the compiler and turned into the most-efficient code (e.g. perhaps even using an EXCH instruction). The latter code is obviously also amenable to use with pointers and floating-point values, unlike the XOR trick. See also questions 3.3b and 10.3.
Additional links: further reading