constant methods vs non-constant methods

[srinivas.symbian]

HI...frdz..
I need to call a non- constant method(which returns some value) from a constant method.. but when i compile it, it is showing an error.." method (non-static) - function call (const method) does not match"..

eg..

int temp_var=0;
void MyClass::test()const
{
temp_var= add(10,20);
}

int MyClass::add(int a, int b)
{ return a+b;}

[srinivas.symbian]

I got solution..
I need to make a local variable (temp_var=0) inside the const method

[danhicksbyron]

"const" for a method (different from a "const" parameter) means that the method has no effect/dependency on its environment and will (presumably) return the same value every time it's called with a given set of parameters. Therefore, the reference to the global variable "temp_var" is not allowed. "add" is validly const, "test" isn't.

In addition, the compiler might choose to still flag "test" as non-const, after moving the temp_var definition inside, since "add" is not declared const, and is referenced from "test". But the compiler probably figures out that "add" is safely const without being told.

[danhicksbyron]

You don't need to pre-assign zero to temp_var, just make it local. Eg, "int temp_var;", or combine with the assignment as "int temp_var = add(10,20);".

Of course, once you make the variable local it can no longer be accessed outside the method.