const

void Blah (const Foo& data) {
   // Function that doesn''t modify data
}
 

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Original post by dMDI
You write const before a parameter when passing by reference to guarantee that the function does not alter the parameter, and simply uses references as an efficient mechanism for passing the parameter.

For example:

void Blah (const Foo& data) {
   // Function that doesn''t modify data
}
  

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Original post by petewood
are compiler implementors allowed to optimise it away?

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Original post by SabreMan
Adding const to a value passed (or returned) by reference isn''t worth worrying about. The idea of const is to enforce that a parameter must not be changed as a side-effect of calling a function. If you pass the parameter by value, it shouldn''t matter, since the callee will construct a local copy and no change will be apparent from the caller code.

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Original post by xropi
What about:

const int Proc3() {
...
}

What''s the point of this? (nothing -- I think)

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quote:

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But this:
const int &Proc4() {
...
}

has meaning for me.

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Original post by Deyja
Const also allows the compiler to make some memory optimizations. For instance, if you pass something by value and const, the compiler doesn''t bother making a copy, because it knows it won''t be changing anyway.

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void foo(const int i)
{
	int& non_const_i = const_cast<int&>(i);
	non_const_i = 10;
}

int main()
{
	int val = 0;
	foo(val);
}  

  
class C
{
public:
	C()
		: counter_(0)
	{}

	void foo() const
	{
		++counter_;
	}
private:
	mutable int counter_;
};

void foo(const C c)
{
	c.foo();
}

int main()
{
	const C c;
	foo(c);
}  

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Original post by petewood
dalleboy: that''s not the question.

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