C language uses macros to implement 2 variable Exchange

Documenting which methods are more pervasive and more efficient does not include methods that use functions, and using pointers is more appropriate if you use functions.

• 　　Using intermediate variables

Shaped as int tmp, TMP = A; A=b; b = tmp;

1 #define SWAP (A, b) {typeof(a) _t=A; A=B; b=_t;}

The only drawback is the need for additional stack space.

• 　　Using arithmetic methods

1 #define SWAP (x, y) (x) = (x) + (y); (y) = (x)-(y);(x) = (x)-(y);

cannot be used, x+y can cause data overflow, then it is finished, and can only operate on basic data types, construction data types cannot be used.

• 　　The cost of brain-different or law

1 #define SWAP (x, y) (x) ^= (y); (y) ^= (x);(x) ^= (y);

Can only be manipulated for basic data types and cannot be used for construction data types.

Then compare the efficiency of 1,3, using 2 macros to run the following code:

int Main (intconstChar *argv[]) {    int0xFFFFFFF ;         int 5 ;     int Ten ;      while (k-- )    {        SWAP (A, b);    }     return 0 ;}

Using time./main timing, the Xor method takes 2.2-2.4s, the intermediate variable method time 0.7-0.8s, the efficiency increases 3 times times.

C language uses macros to implement exchange of 2 variables