Question

Is there any benefit (or conversely, cost) to passing a parameter by const value in the function signature?

So:

void foo( size_t nValue )
{
    // ...

vs

void foo( const size_t nValue )
{
    // ...

The only reason for doing this that I can think of would be to ensure the parameter wasn’t modified as part of the function although since it has not been passed by reference there would be no wider impact outside the function.

Answer 1

Of course there is. You can’t modify nValue inside the function.

As with const-ness in general, it’s not a security measure, since you can cast it away, but a design matter.

You’re explicitly telling other programmers that see your code –

“I will not modify nValue inside this function

and programmers that maintain or change your code

“If you want to modify nValue, you’re probably doing something wrong. You shouldn’t need to do this”.