Big parameter passed by value

In C and C++, parameters are passed by value, that is, a call copies the contents of the actual parameter to the formal parameter as if by assignment. When a parameter is large, this copy is expensive. Usually it is better to pass arguments bigger than 16 bytes by reference, that is, to pass a pointer to the object rather than the object itself.

In C++, you can declare a REF parameter by replacing the formal parameter type T with T&. The call arguments and subroutine body are unaffected. In C, you can convert a by-value parameter to a by-reference parameter as follows. Declare the parameter as type T* rather than type T, replace all uses of the formal parameter "x" with "(*x)", and replace the corresponding argument V at each call by its address, &V.

Warning: Arguments passed by reference are modified if the called routine modifies the reference parameter. Before replacing a by-value parameter with a by-reference parameter, make sure there are no assignments to the formal parameter.

          
typedef struct {
    int x[10];
} T;

int add_up(T p) { // Better is int add_up(T &p)
    int i, total = 0;
    for (i = 0; i < 10; i++) {
        total += p.x[i];
    }
    return total;
}