What does const after function header do?

Question

I saw following code on c++ reference: bool operator() (const int& lhs, const int&rhs) const What does the last const do?

score 1 · Answer 1 · answered Apr 17 '14 at 19:25

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It means the function (operator) does not change the object.

answered Apr 17 '14 at 19:25

wallyk

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score 1 · Accepted Answer · answered Apr 17 '14 at 19:26

From the Const Correctness tutorial:

If you have a const object, you don't want to call methods that can change the object, so you need a way of letting the compiler know which methods can be safely called. These methods are called "const functions", and are the only functions that can be called on a const object. Note, by the way, that only member methods make sense as const methods. Remember that in C++, every method of an object receives an implicit this pointer to the object; const methods effectively receive a const this pointer.

It might be worthwhile (spoiler: it is) to read through the whole article if you're new to the concept of constness.

Herb Sutter's GotW articles are quite good, too. See [GotW #6](http://gotw.ca/gotw/006.htm). — Void - Othman, Apr 17 '14 at 20:06

score 1 · Answer 3 · answered Apr 17 '14 at 19:26

1

Effectively makes the "this" pointer a pointer to a const object. It means that members of the object cannot be modified in that method, nor can that method be invoked on a non-const object.

answered Apr 17 '14 at 19:26

Ben

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What does const after function header do?

3 Answers3