What does "const" mean (in context) at the end of a function definition? [duplicate]

Question

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What is the meaning of a const at end of a member function?

If my class definition is as follows:

type CLASS::FUNCTION(int, const char*) const 

What does the last const after the closing bracket mean, and how do I apply it to the function:

type CLASS::FUNCTION(int var1, const char* var2) {  } 

Answer 1

It means that this function does not modify the observable state of an object.

In compiler terms, it means that you cannot call a function on a const object (or const reference or const pointer) unless that function is also declared to be const. Also, methods which are declared const are not allowed to call methods which are not.

Update: as Aasmund totally correctly adds, const methods are allowed to change the value of members declared to be mutable.

For example, it might make sense to have a read-only operation (e.g. int CalculateSomeValue() const) which caches its results because it's expensive to call. In this case, you need to have a mutable member to write the cached results to.

I apologize for the omission, I was trying to be fast and to the point. :)

Answer 2

const at the end of the function means it isn't going to modify the state of the object it is called up on ( i.e., this ).

type CLASS::FUNCTION(int, const char*) const ; // Method Signature  type CLASS::FUNCTION(int var1, const char* var2) const {  } 

You need to mention the keyword const at the end of the method definition too. Also note that only member functions can have this non-modifier keyword const at their end.