"cannot convert from 'class X *' to 'class X'" ??

hard2clone · #1 03-Aug-2005, 13:22

What's the problem here? when i try to create a new instance of my class Signature it's giving me the following error:

c:\PredicateLogicTrainer\signature.h(104) : error C2440: 'initializing' : cannot convert from 'class Signature *' to 'class Signature'
No constructor could take the source type, or constructor overload resolution was ambiguous
Error executing cl.exe.

main.exe - 1 error(s), 0 warning(s)

it refers to the following line:

CPP / C++ / C Code:

Signature signature = new Signature(name, unaryArray, binaryArray, constantArray) ;

I'm lost... is this the right way to create a class??

Here's the full code:

CPP / C++ / C Code:

#include <iostream>
#include <fstream>
using namespace std;
#ifndef SIGNATURE_H
#define SIGNATURE_H

class Signature
{
public:
	Signature(		
		string nName, 
		string unaryRels[3],
		string binaryRels[3],
		string constants[3]);
	Signature();


Signature makeSignature(string newName, int unaryRs, int binaryRs, int constants) {


	string name = "Untitled";
	cout << "\nThank you for creating a signature. So, what would you like to call this signature?";
	cin >> name;
	if (name == ""){
		name = "untitled";
	}


	string numberTail = "th";

	string unaryArray[3]; 

	for (int u = 0; u < unaryRs; u++) {
		cout << "\nPlease enter the name of the " << u + 1;
		if (u == 0) {
			numberTail = "st";
		}
		if (u == 1) {
			numberTail = "nd";
		}
		if (u == 2) {
			numberTail = "rd";
		}
		cout << numberTail << " unary relation symbol. If you don't want one, just press Enter.\n";
		cin >> unaryArray[u];
	}
	
	
//	numberTail = "th";

	string binaryArray[3];
		
	for (int b = 0; b < binaryRs; b++) {
		cout << "\nPlease enter the name of the " << b + 1;
		if (b == 0) {
			numberTail = "st";
		}
		if (b == 1) {
			numberTail = "nd";
		}
		if (b == 2) {
			numberTail = "rd";
		}
		cout << numberTail << " binary relation symbol. If you don't want one, just press Enter.\n";
		cin >> binaryArray[b];
	}

	string constantArray[3];
		
	for (int c = 0; c < constants; c++) 
	{
		cout << "\nPlease enter the name of the " << c + 1;
		if (c == 0) {
			numberTail = "st";
		}
		if (c == 1) {
			numberTail = "nd";
		}
		if (c == 2) {
			numberTail = "rd";
		}
		cout << numberTail << " constant. If you don't want one, just press Enter.\n";
		cin >> constantArray[c];
	}


	for (int a = 0; a< 3; a++) {
		cout << "\n\nThe arrays look like this: ";
		cout << "\n" << unaryArray[a];
		cout << "\n" << binaryArray[a];
		cout << "\n" << constantArray[a];
	}
	
	



//	for (int c = 0, c < constants, c++) {

//		cout << "\nPlease enter the "



Signature signature = new Signature(name, unaryArray, binaryArray, constantArray) ;

return signature;
};

};

#endif

CMan · #2 03-Aug-2005, 13:59

in C++, the "new" keyword is used to create pointers as far as I know, so maybe you should do:

Code:

Signature signature(name, unaryArray, binaryArray, constantArray) ;

instead of

Code:

Signature signature = new Signature(name, unaryArray, binaryArray, constantArray) ;

It's different from Java and C# where you have to use new to declare an object of a class.

Dave Sinkula · #3 03-Aug-2005, 14:04

Quote:

Originally Posted by hard2clone

CPP / C++ / C Code:

Signature makeSignature(string newName, int unaryRs, int binaryRs, int constants) {
// ...
Signature signature = new Signature(name, unaryArray, binaryArray, constantArray) ;

return signature;
}

How about this?

CPP / C++ / C Code:

Signature makeSignature(string newName, int unaryRs, int binaryRs, int constants) {
// ...
return Signature(name, unaryArray, binaryArray, constantArray) ;
}

hard2clone · #4 03-Aug-2005, 14:07

Quote:

Originally Posted by CMan

in C++, the "new" keyword is used to create pointers as far as I know, so maybe you should do:

Code:

Signature signature(name, unaryArray, binaryArray, constantArray) ;

instead of

Code:

Signature signature = new Signature(name, unaryArray, binaryArray, constantArray) ;

It's different from Java and C# where you have to use new to declare an object of a class.

Thanks buddy, You're a star!!

I've got other errors now, but that one was killing me.

Cheers!

hard2clone · #5 03-Aug-2005, 14:30

Now, the above works!!

However, in the main file, I want to create a signature... so naturally i type:

CPP / C++ / C Code:

Signature s; // to declare a signature called s
s.makeSignature (3, 3, 3); // btw, i changed the parameters to the makeSignature above to only the last three, as i gain the fourth parameter from a cin call

but i get the following error:

Linking...
main.obj : error LNK2001: unresolved external symbol "public: __thiscall Signature::Signature(void)" (??0Signature@@QAE@XZ)
main.obj : error LNK2001: unresolved external symbol "public: __thiscall Signature::Signature(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class st
d::allocator<char> > * const,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > * const,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > * const)" (??0Signature@@QAE@V?$basi
c_string@DU?$char_traits@D@std@@V?$allocator@D@2@@ std@@QAV12@11@Z)
Debug/main.exe : fatal error LNK1120: 2 unresolved externals
Error executing link.exe.

Note, this is not a compile error, it's a linking error.... i don't have a clue what that is...

Dave Sinkula · #6 03-Aug-2005, 15:44

I believe it's the linker's way of saying, "Hey, buddy! You told me to expect these:"

CPP / C++ / C Code:

  Signature(    
    string nName, 
    string unaryRels[3],
    string binaryRels[3],
    string constants[3]);
  Signature();

"Where are they? What gives?"

In other words, you need to define these functions. Mere declarations are not enough. Otherwise every one of us would have written this, run it, and quit coding to retire on some beach:

CPP / C++ / C Code:

int SendMeMillions(int count);

CMan · #7 03-Aug-2005, 16:06

Quote:

Originally Posted by hard2clone

Thanks buddy

No problem.

For the linker problem though, I agree with Dave. Do something like this for each undefined function:

CPP / C++ / C Code:

    Signature() 
    {
         //Your implementation here, or leave it empty if no initialization is required.
    }; //see, we implemented the ctor

Quote:

Originally Posted by Dave Sinkula

Otherwise every one of us would have written this, run it, and quit coding to retire on some beach:

CPP / C++ / C Code:

int SendMeMillions(int count);

CPP / C++ / C Code:

int SendMeMillions(int count)
{  ofstream fout("MyPocket");
   fout<<count;
}

there we go

05gtp · #8 03-Aug-2005, 16:32

this compiles, links and executes...
I agree, you have no member function bodies, unless you have them in a seperate header file?

CPP / C++ / C Code:


#ifndef _SIGNATURE_H_INCLUDED
#define _SIGNATURE_H_INCLUDED

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

#pragma once

class Signature
{
public:
	Signature(void) {}
	Signature(string nName, string unaryRels[3], string binaryRels[3], string constants[3]) {}
	virtual ~Signature(void) {}

	Signature Signature::makeSignature(string newName, int unaryRs, int binaryRs, int constants)
	{

		string name = "Untitled";
		cout << "\nThank you for creating a signature.\nSo, what would you like to call this signature?  ";
		cin >> name;

		string postfix;
		if (name == "") name = "untitled";

		string unaryArray[3];
		for (int u = 0; u < unaryRs; u++) {
			cout << "\nPlease enter the name of the " << u + 1;
			if (u == 0) postfix = "st";
			if (u == 1) postfix = "nd";
			if (u == 2) postfix = "rd";
			cout << postfix << " unary relation symbol.\nIf you don't want one, just press Enter.\n";
			cin >> unaryArray[u];
		}

		string binaryArray[3];
		for (int b = 0; b < binaryRs; b++) {
			cout << "\nPlease enter the name of the " << b + 1;
			if (b == 0) postfix = "st";
			if (b == 1) postfix = "nd";
			if (b == 2) postfix = "rd";
			cout << postfix << " binary relation symbol.\nIf you don't want one, just press Enter.\n";
			cin >> binaryArray[b];
		}

		string constantArray[3];
		for (int c = 0; c < constants; c++) {
			cout << "\nPlease enter the name of the " << c + 1;
			if (c == 0) postfix = "st";
			if (c == 1) postfix = "nd";
			if (c == 2) postfix = "rd";
			cout << postfix << " constant.\nIf you don't want one, just press Enter.\n";
			cin >> constantArray[c];
		}

		for (int a = 0; a < 3; a++) {
			cout << "\n\nThe arrays look like this: ";
			cout << "\n" << unaryArray[a];
			cout << "\n" << binaryArray[a];
			cout << "\n" << constantArray[a];
			cout << "\n";
		}

		Signature signature(name, unaryArray, binaryArray, constantArray);

		return signature;
	}
};

#endif // _SIGNATURE_H_INCLUDED

OR, quick edit, I prefer this one... Up2U.

CPP / C++ / C Code:


#ifndef _SIGNATURE_H_INCLUDED
#define _SIGNATURE_H_INCLUDED

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

#pragma once

class Signature
{
public:
	Signature(void) {}
	Signature(string nName, string unaryRels[3], string binaryRels[3], string constants[3]) {}
	virtual ~Signature(void) {}

	void Signature::Menu(const unsigned int cnt, const string arrType)
	{
		string postfix;
		cout << "\nPlease enter the name of the " << cnt + 1;
		if (cnt == 0) postfix = "st";
		if (cnt == 1) postfix = "nd";
		if (cnt == 2) postfix = "rd";
		cout << postfix << " " << arrType << " relation symbol.\nIf you don't want one, just press Enter.\n";
	}

	Signature Signature::makeSignature(string newName, int unaryRs, int binaryRs, int constants)
	{

		string name = "Untitled";
		cout << "\nThank you for creating a signature.\nSo, what would you like to call this signature?  ";
		cin >> name;

		if (name == "") name = "untitled";

		string unaryArray[3];
		for (int u = 0; u < unaryRs; u++) {
			Menu(u, "unary");
			cin >> unaryArray[u];
		}

		string binaryArray[3];
		for (int b = 0; b < binaryRs; b++) {
			Menu(b, "binary");
			cin >> binaryArray[b];
		}

		string constantArray[3];
		for (int c = 0; c < constants; c++) {
			Menu(c, "constant");
			cin >> constantArray[c];
		}

		for (int a = 0; a < 3; a++) {
			cout << "\n\nThe arrays look like this: ";
			cout << "\n" << unaryArray[a];
			cout << "\n" << binaryArray[a];
			cout << "\n" << constantArray[a];
			cout << "\n";
		}

		Signature signature(name, unaryArray, binaryArray, constantArray);

		return signature;
	}
};

#endif // _SIGNATURE_H_INCLUDED

Dave Sinkula · #9 03-Aug-2005, 16:49

Hopefully what was posted is not actually in a header. If so, I'd recommend to the OP to quit now and learn how it's supposed to be done -- no code in headers! (With exceptions for templates at least.)

And no using namespace std; in headers either!

05gtp · #10 03-Aug-2005, 16:58

All classes should have a header file of the class definition and a cpp source file that contains the code. This is how I solved it, but I put it back as it was originally, roughly, posted. Also, avoid the namespace issue of name clashing, such as std::count.

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"cannot convert from 'class X *' to 'class X'" ??

got this to work

Dave, I agree...