Thread: Vector of references

I think my understanding of references is incomplete. I would like to create a vector of references to a type, the purpose being to gain the benefits of a vector without having to copy each element or use pointers. Why is it not possible to create a vector of references? (I tried with Borland 5.5.1 on Win32 and got a slew of errors referring to "Cannot define a pointer or reference to a reference in int main()").

My code:

Code:

#include <iostream>
#include <vector>
using namespace std;

class MyTest {

	public:
	MyTest() {
		cout << "Creating a new MyTest object!" << endl;
	}
	MyTest( const MyTest& ) {
		cout << "Creating a new MyTest object!" << endl;
	}

};

int main() {

	MyTest a;
	MyTest b;

	vector< MyTest& > baz;
	baz.push_back( a );
	baz.push_back( b );

}

Originally posted by Brighteyes
Because all references must refer to something. The references in your vector don't have anything to alias, so it's an error.

Do they not refer to "a" and "b" (MyTest objects above)? As long as the vector is within the same scope as a and b (i.e., they do not fall out of scope as a result of being local), are references to those objects not valid?

Also, the implementation probably uses references too and a reference to a reference is illegal, but a reference to a pointer is not, that's why you can make a vector of pointers.

stoned_coder:
just as you cannot create an array of references so you cannot create a vector of them

I recognize that this is true, but I'm trying to determine why. I do not see the inherent problem with such a construct (in theory) as long as the objects referred to are still in scope, but I am obviously missing something. Or is it a problem with trying to implement such a thing?

Perhaps the answer lies in knowing exactly what a reference is? Is it merely a new name for something? A compiler construct that has no actual value? (I.e. an int is a datatype that takes up 4 bytes, an int* is a pointer to such a value, and takes up some other amount of memory, but how much memory and what exactly is an int&? Does it exist in the same way?)