I am trying to compile 2 classes in C++ with the following command:
g++ Cat.cpp Cat_main.cpp -o Cat
But I receive the following error:
Cat.cpp:10:10: error: variable ‘Cat Joey’ has initializer but incomplete type
Could someone explain to me what this means? What my files basically do is create a class (Cat.cpp) and create an instance (Cat_main.cpp). Here is my source code:
Cat.cpp:
#include <iostream>
#include <string>
class Cat;
using namespace std;
int main()
{
Cat Joey("Joey");
Joey.Meow();
return 0;
}
Cat_main.cpp:
#include <iostream>
#include <string>
using namespace std;
class Cat
{
public:
Cat(string str);
// Variables
string name;
// Functions
void Meow();
};
Cat::Cat(string str)
{
this->name = str;
}
void Cat::Meow()
{
cout << "Meow!" << endl;
return;
}
This question is related to
c++
class
compiler-construction
You use a forward declaration when you need a complete type.
You must have a full definition of the class in order to use it.
The usual way to go about this is:
1) create a file Cat_main.h
2) move
#include <string>
class Cat
{
public:
Cat(std::string str);
// Variables
std::string name;
// Functions
void Meow();
};
to Cat_main.h. Note that inside the header I removed using namespace std; and qualified string with std::string.
3) include this file in both Cat_main.cpp and Cat.cpp:
#include "Cat_main.h"
It's not related to Ken's case directly, but such an error also can occur if you copied .h file and forgot to change #ifndef directive. In this case compiler will just skip definition of the class thinking that it's a duplication.
You cannot define a variable of an incomplete type. You need to bring the whole definition of Cat into scope before you can create the local variable in main. I recommend that you move the definition of the type Cat to a header and include it from the translation unit that has main.
Sometimes, the same error occurs when you forget to include the corresponding header.
I got a similar error and hit this page while searching the solution.
With Qt this error can happen if you forget to add the QT_WRAP_CPP( ... ) step in your build to run meta object compiler (moc). Including the Qt header is not sufficient.
Source: Stackoverflow.com