best algorithm for swapping?

this swapping trick is sometimes dangerous, I have seen a a wrong quicksort program using this swap generates wrong results. But a usual swap generates correct program.

Respect to speed, the compiler sometimes generates faster code if we use a tmp variable.

use tmp = a; a = b; b = tmp;

a^=b^=a^=b; probably crashes because it invokes the dreaded undefined behaviour. The rule it breaks is that it modifies a twice without an intervening sequence point. It can be fixed by inserting some sequence points - for example, with the comma operator:

a ^= (b ^= a ^= b, b);`

Or by breaking it up into multiple statements:

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

It is still, however, usually a bad method for swapping variables - several of the other answers and comments have adequately explained why.

See http://en.wikipedia.org/wiki/Swap_(computer_science) .

Using a temporary variable generates more overhead, but is more stable than the XOR swap algorithm and parallel computing renders it faster than XOR swap.

See the first code example of http://www.ibm.com/developerworks/linux/library/l-metaprog1.html for a solid implementation of using a temporary variable for swapping.