in
int salary() const { return mySalary; }
as far as I understand const is for this pointer, but I'm not sure. Can any one tell me what is the use of const over here?
Thanks
+7
A:
Sounds like you've got the right idea, in C++ const on a method of an object means that the method cannot modify the object.
For example, this would not be allowed:
class Animal {
int _state = 0;
void changeState() const {
_state = 1;
}
}
Alex Black
2010-01-08 02:55:40
This syntax is only valid for C++0x
ergosys
2010-01-08 03:06:21
Which syntax? I haven't typed any C++ in a while, so perhaps I got something slightly wrong, no guarantees it compiles, but overlooking any mistakes I'm sure you get the general idea, and the general idea is part of regular C++.
Alex Black
2010-01-08 03:09:32
I could be mistaken, I was using MSVC++ version 6 (years ago), perhaps it didn't conform to the spec, does Microsoft ever do anything like that? ;)
Alex Black
2010-01-08 03:12:46
Under C++-98: §9.3.3: "A nonstatic member function may be declared const, volatile, or const volatile. These cv-qualifiers affect the type of the this pointer (9.3.2)." Therefore, that code snippet should produce an error.
greyfade
2010-01-08 03:38:40
I was referring to the instance member initialization, this is new for C++0x.
ergosys
2010-01-08 04:16:08
Alex has been doing C#, I'd guess. But the idea is the same.
Hans Passant
2010-01-08 04:59:21
@ergosys: ah, thanks. I've been doing C# and Scala recently, the C++ knowledge is getting overwritten!
Alex Black
2010-01-08 13:34:07
A:
It's a const method. It means that it won't modify the member variables of the class nor will it call non-const methods. Thus:
const foo bar;
bar.m();
is legal if m is a const method but otherwise wouldn't be.
Jason
2010-01-08 02:55:48
+5
A:
When the function is marked const it can be called on a const pointer/reference of that class. In effect it says This function does not modify the state of the class.
Igor Zevaka
2010-01-08 02:56:06
A:
It means that function can be called on a const object; and inside that member function the this pointer is const.
Terry Mahaffey
2010-01-08 02:56:22
A:
It's a const member function. It's a contract that the function does not change the state of the instance.
more here: http://www.fredosaurus.com/notes-cpp/oop-memberfuncs/constmemberfuncs.html
mmattax
2010-01-08 02:57:31