Programming Forums > Application Development > C++

hbe02 · Apr 21st, 2006, 8:51 AM

Im writing a class which i want to give 2 contructors, one constructor has input parameters and one doesnt. Is this the correct way of doing things.
I only recieve a warning:

Quote:

warning C4520: 'RTPpacket' : multiple default constructors specified

Is there something i should add or specify when writing a class with 2 constructors to avoid such warnings?
thanks.

nnxion · Apr 21st, 2006, 9:31 AM

I'm not sure when that occurs without seeing your code.
Here is an example of how it does work.

(Toggle Plain Text)

#include <iostream>
#include <string>

using namespace std;

class Packet
{
	private:
		int packetID;
		string packetName;
	public:
		Packet();
		Packet(int);
		Packet(int, string);
		void PrintAttributes();
};

Packet::Packet()
{
	packetID = 0;
	packetName = "no name";
}

Packet::Packet(int id)
{
	packetID = id;
	packetName = "no name";
}

Packet::Packet(int id, string str)
{
	packetID = id;
	packetName = str;
}

void Packet::PrintAttributes()
{
	cout << "PacketID = " << packetID << endl;
	cout << "PacketName = " << packetName << endl << endl;
}

int main()
{
	Packet packet1;
	packet1.PrintAttributes();

	Packet packet2(1);
	packet2.PrintAttributes();

	Packet packet3(2, "myPacket");
	packet3.PrintAttributes();

	return 0;
}

grumpy · Apr 21st, 2006, 9:37 AM

Some compilers will complain about multiple default constructors (or ambiguous function calls) in a circumstance like;

(Toggle Plain Text)

class Something
{
    public:

        Something();
        Something(int x = 0, int y = 0);
};

as both constructors can be invoked without arguments (i.e. both are default constructors).

It is more common for a compiler to complain when attempting to use the class in this case (as that's when the compiler realises there are two candidates that can be called), but some smarter (?) ones do actually complain when compiling the class declaration.

Another possible cause of such a message is accidentally providing two constructors that take no arguments;

(Toggle Plain Text)

class Something
{
    public:

        Something();

        //   and later
        Something();     // Whoops!
};

hbe02 · Apr 21st, 2006, 11:49 AM

Thanks for your help guys.
I recieved the warning because i defined the contructors inside the class. the warning no longer appeared when i only defined the contructors return type parameters in the class and wrote their implemented code outside. just like nnxion wrote it.

Apr 21st, 2006, 9:31 AM	#2
nnxion Programming Guru Join Date: Jun 2005 Location: elemental plane Posts: 1,429 Rep Power: 5	I'm not sure when that occurs without seeing your code. Here is an example of how it does work. (Toggle Plain Text) #include <iostream> #include <string> using namespace std; class Packet { private: int packetID; string packetName; public: Packet(); Packet(int); Packet(int, string); void PrintAttributes(); }; Packet::Packet() { packetID = 0; packetName = "no name"; } Packet::Packet(int id) { packetID = id; packetName = "no name"; } Packet::Packet(int id, string str) { packetID = id; packetName = str; } void Packet::PrintAttributes() { cout << "PacketID = " << packetID << endl; cout << "PacketName = " << packetName << endl << endl; } int main() { Packet packet1; packet1.PrintAttributes(); Packet packet2(1); packet2.PrintAttributes(); Packet packet3(2, "myPacket"); packet3.PrintAttributes(); return 0; } #include <iostream> #include <string> using namespace std; class Packet { private: int packetID; string packetName; public: Packet(); Packet(int); Packet(int, string); void PrintAttributes(); }; Packet::Packet() { packetID = 0; packetName = "no name"; } Packet::Packet(int id) { packetID = id; packetName = "no name"; } Packet::Packet(int id, string str) { packetID = id; packetName = str; } void Packet::PrintAttributes() { cout << "PacketID = " << packetID << endl; cout << "PacketName = " << packetName << endl << endl; } int main() { Packet packet1; packet1.PrintAttributes(); Packet packet2(1); packet2.PrintAttributes(); Packet packet3(2, "myPacket"); packet3.PrintAttributes(); return 0; } __________________ "Employ your time in improving yourself by other men's writings, so that you shall gain easily what others have labored hard for." -- Socrates

Apr 21st, 2006, 9:37 AM	#3
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Some compilers will complain about multiple default constructors (or ambiguous function calls) in a circumstance like; (Toggle Plain Text) class Something { public: Something(); Something(int x = 0, int y = 0); }; class Something { public: Something(); Something(int x = 0, int y = 0); }; as both constructors can be invoked without arguments (i.e. both are default constructors). It is more common for a compiler to complain when attempting to use the class in this case (as that's when the compiler realises there are two candidates that can be called), but some smarter (?) ones do actually complain when compiling the class declaration. Another possible cause of such a message is accidentally providing two constructors that take no arguments; (Toggle Plain Text) class Something { public: Something(); // and later Something(); // Whoops! }; class Something { public: Something(); // and later Something(); // Whoops! };

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Apr 21st, 2006, 11:49 AM	#4
hbe02 Hobbyist Programmer Join Date: Mar 2006 Location: Lebanon Posts: 148 Rep Power: 3	Thanks for your help guys. I recieved the warning because i defined the contructors inside the class. the warning no longer appeared when i only defined the contructors return type parameters in the class and wrote their implemented code outside. just like nnxion wrote it.

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Programming Forums > Application Development > C++

Multiple constructors