"Const &" modifier input parameter usage Summary

For non-Internal data type input parameters, the "value transfer" method should be changed to "const reference Transmission
To improve efficiency. For example, change void func (A) to void func (const A & ).

For internal data type input parameters, do not change the "value transfer" method to "const reference transfer ".
Otherwise, the function can not improve the efficiency, but also reduce the comprehensibility of the function. For example, void func (int x) is not
It should be changed to void func (const Int & X ).

11.1.1 use const to modify function parameters
If a parameter is used for output, No matter what data type it is, whether it uses "pointer transmission" or "Reference
If the parameter is passed, the const parameter cannot be added; otherwise, the output function is lost.
Const can only modify the input parameters: