const

[sujitnag]

what are the diff between
1)const return_type func(){}
2) return_type func()const{}

as far I understand 1st one return type is const like const int etc.

but 2nd one is not clear to me.
so if you help me to understand 2nd on.
thanx.

[Disch]

#1: The item being returned from the function is const.
#2: The function itself is const, meaning it does not modify the calling object. IE: it can safely be called with a const object.


Example:

int data;

class Example
{
public:
    int& foo() const { return data; }
    const int& bar() { return data; }
};

int main()
{
    Example nc;  // a non-const object
    const Example cc;  // a const object

    // Example of #1:
    nc.foo() = 5;   // OK, return value is non-const, so we can assign it.
    nc.bar() = 5;   // ERROR, return value is const, so we can't assign it.

    // Example of #2:
    nc.foo();  // OK
    nc.bar();  // OK

    cc.foo();  // OK, object is const, but function is also const
    cc.bar();  // ERROR, object is const, so cannot call a non-const function
}

[sujitnag]

I can understood.
but
nc.foo() = 5;

is new.

object.funtion()=value;

plz can you explain this line.

[Disch]

foo() returns a reference (that's what the & symbol means).

A reference is basically an alias for an existing variable.

Since foo() returns a reference to 'data', nc.foo() = 5; will assign 5 to the 'data' variable.

I can't really explain in any more detail than that. Perhaps read a tutorial on references to gain a better understanding.

[sujitnag]

thankx;
actually I overlook the return type; so it make me difficult to understand.

once again thx.
every thing clear to me.