int TheFunction() const
{
return 0;
}
question about const
Author
What does it mean when const is used in the following way?
*clips answer which he said could be wrong, and ended up being wrong*
[edited by - MaulingMonkey on August 7, 2003 12:19:22 AM]
[edited by - MaulingMonkey on August 7, 2003 12:19:22 AM]
"int blah() const" has to be a member of some class. The const means that the function won''t modify the contents of the object on which it operates.
say you have an operator+ for a complex number class...
Complex a, b, c;
c = a+b;
a and b aren''t modified. a''s method operator+ returns a temp object that gets assigned to c. operator+ (...) const is used to signify that the function won''t modify a''s member variables. I forget exactly when this is required...
Complex a, b, c;
c = a+b;
a and b aren''t modified. a''s method operator+ returns a temp object that gets assigned to c. operator+ (...) const is used to signify that the function won''t modify a''s member variables. I forget exactly when this is required...
quote:Original post by Nypyren
I forget exactly when this is required...
Say you have a constant that gets promoted to your class. Eg. a string:
string a = " world";
string x = "hello" + a;
"hello" would be promoted to a constant string type, so operator+ must be a const member.
The following statement is true. The previous statement is false.Shameless promotion:
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Is it valid for a const function to return a reference to a member variable and then have the reference edited outside of the function?
I would assume so.
A const function could return a pointer, so the value could be changed. I would assume that it could do the same for a reference. But, I could be wrong...
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A const function could return a pointer, so the value could be changed. I would assume that it could do the same for a reference. But, I could be wrong...
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MyClass& MyClass::returnObject(void)const //WRONG{ return(*this);}// error C2440: 'return' : 'const class MyClass' cannot be // converted to 'class MyClass &'.const MyClass& MyClass::returnObject(void)const //RIGHT{ return(*this);}If you would be allowed to return a non-const reference your data could be modified despite the member function being const. Thus it's not legal.
[edited by - Wildfire on August 8, 2003 3:09:48 AM]
Wildfire, here''s something that''ll surprise you:
Compiles OK, output is: 4,8
struct T { T(int& b) : a(b) {} int& a; int& getA() const { return a; }};int main() { int x = 4, y = 8; const T t(x); //note: t is const. cout << t.a << '',''; t.getA() = y; cout << t.a;} Compiles OK, output is: 4,8
civguy, that''s not the same thing. Wildfire is returning (*this) which is a const variable, so the function''s return type has to be const as well. Your member variable ''int a'' is not const, and you do not modify it inside getA(), so all is well. Also it doesn''t matter that t is const, because you are not [directly] modifying it, you are using an accessor function.
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