C++ - What does const represent here?

Question

If I get a C++ statement as follows:

double getPrice() const;

What doesn const represent here?

Thanks.

score 7 · Accepted Answer · answered Feb 24 '11 at 14:21

7

This is for member functions (in classes or structs). It means that the method won't change the state of the instance it operates on (won't change any member variables for example).

answered Feb 24 '11 at 14:21

PeterK

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Unless they were declared mutable – Armen Tsirunyan Feb 24 '11 at 14:27
@Armen Tsirunyan: If they are declared mutable then technically they not part of the objects logical state. – Martin York Feb 24 '11 at 16:48
I was complaining about the phrase "won't change any member variables for example" – Armen Tsirunyan Feb 24 '11 at 17:05

score 3 · Answer 2 · answered Feb 24 '11 at 14:26

When you call nonstatic member functions, you always call it on some object, right? That object is passed (implicitly) as a parameter. For example, if GetPrice is the method of class X, then it has an implicit parameter of type X&. Then the method is const, the implicit argument is of type const X&, therefore the member function cannot change any data member of the object on which it was invoked, UNLESS the data member was declared mutable.

score 2 · Answer 3 · answered Feb 24 '11 at 14:21

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It signifies that it will not change the members of the class as a side effect.

answered Feb 24 '11 at 14:21

Daniel A. White

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Trinidad · Answer 4 · 2011-02-24T14:31:04.057

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const means that getPrice() won't modify instance fields, except those explicitly declared as mutable.

edited Feb 24 '11 at 14:31

answered Feb 24 '11 at 14:22

Trinidad

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A binary dump is not guaranteed to be the same before and after. The method is permitted to change members declared mutable. – Alex Deem Feb 24 '11 at 14:27

C++ - What does const represent here?

4 Answers4