why cannot convert parameter 1 from 'ICommand *' to 'ICommand *&'?

[csoapy]

i can not pass a pointer to ICommand to a Test(ICommand * &p), and why got this error? thx!

#include <list>

class ICommand{public : virtual void vfunc(){}};
class CSession : public ICommand{};

void Test(ICommand * & pCommand){delete pCommand; pCommand = NULL;}

int main(int argc, char *argv[])
{
	ICommand * pCommand = new ICommand();
	CSession * pSession = new CSession();

	std::list<ICommand*> commands;	commands.push_back(pCommand);
	std::list<CSession*> sessions;	sessions.push_back(pSession);

	Test(*commands.begin());

	ICommand *p = dynamic_cast<ICommand*>(*sessions.begin());
	Test(p);

	sessions.push_back(new CSession());

	Test(dynamic_cast<ICommand*>(*sessions.begin())); // cannot convert parameter 1 from 'ICommand *' to 'ICommand *&'

	return 0;
}

[vlad from moscow]

For a temporary object const reference is required.

[csoapy]

a const reference ? but there is no one parameter is const.

[vlad from moscow]

I am repeating the second time: for a temporary object const reference required.

Here

Test(dynamic_cast<ICommand*>(*sessions.begin()));

the argument is a temporary object.

[csoapy]

sorry, i can't understand what u say, could u show ur code that's correctly?

[Zhuge]

Test() takes a reference, but you are passing it a temporary variable; specifically, the result of your dynamic_cast. This isn't allowed. You need to make Test() take a const reference, or first assign the dynamic_cast result to a variable before passing it to Test().

[csoapy]

i see, Thank you vlan, Thank you Zhuge!

#include <iostream>

int GetInt(){ return 200; }

void Test(int & a){ a = 100; }

int main(int argc, char *argv[])
{
	int i = GetInt();

	Test(i); // works

	//Test(GetInt());	// cannot convert parameter 1 from 'int' to 'int &'

	return 0;
}

[Zhuge]

Exactly. Good to see you understand. :)