Const usage in C + + (3)--Reference parameter problem

The reference parameter usage for C + + functions is probably this:

void swap (int &a,int &b) {    int temp = A;    A = b;    b = temp;}

A simple function for exchanging two int numbers, when calling the function, such as

int i = 3;int j = 4;swap (i,j);

The result is i=4,j=3. Because the reference parameter is actually an alias of an argument, manipulating the reference parameter is the same as passing a pointer. If you use the normal int parameter, you will not get this effect.

If you use the const modifier parameter, such as const int &a, to indicate that the parameter cannot be changed, there is a problem that requires special attention.

int incr (int &val) {    return ++val;} int main () {short    v1 = 0;    const INT v2 =;    int v3 = incr (v1); V1 is a short type, and the formal parameter is int type    v3 = incr (v2);     V2 is a const, and the formal parameter is non-const    return 0;}

As I've described earlier, a const variable cannot be assigned to a const variable, so a const-type V2 cannot be passed to a non-const parameter.

A non-const reference parameter can only be associated with a non-const object of exactly the same type, so the short type V1 cannot be passed to an int parameter. Therefore, a formal parameter that does not modify the corresponding argument should be defined as a const reference. If such a parameter is defined as a non-const reference, the use of the function is limited.

Const usage in C + + (3)--Reference parameter problem