C++ const keyword - use liberally?

Question

In the following C++ functions:

void MyFunction(int age, House &purchased_house)
{
    ...
}


void MyFunction(const int age, House &purchased_house)         


        

Answer 1

I recommend reading Herb Sutter. Exceptional C++. There is a chapter "Const-Correctness".

"In fact, to the compiler, the function signature is the same whether you include this const in front of a value parameter or not."

It means that this signature

void print(int number);

is effectively the same as this:

void print(int const number);

So, to the compiler there is no difference how you declare a function. And you can't overload it by putting the const keyword in front of a pass by value parameter.

Read further, what Herb Sutter recommends:

"Avoid const pass-by-value parameters in function declarations. Still make the parameter const in the same function's definition if it won't be modified."

He recommends to avoid this:

void print(int const number);

Because that const is confusing, verbose and redundant.

But in the definition, you should do that (if you won't change the parameter):

void print(int const number)
{
   // I don't want to change the number accidentally here
   ...
}

So, you'll be sure that even after 1000 lines of function's body you always have the number untouched. The compiler will prohibit you from passing the number as a non-const reference to another function.