If you're a C++ developer, you may have come across the error message "pointer to incomplete class type is not allowed." This error can be frustrating, especially if you're not sure what it means or how to fix it. In this guide, we'll explain the meaning behind this error message and provide a step-by-step solution for resolving it.
What is an Incomplete Class Type?
An incomplete class type is a class that has been declared but not defined. In other words, the class has been declared, but its members have not been defined. This can happen when a header file declares a class, but the implementation file does not define it.
What Causes the 'Pointer to Incomplete Class Type is Not Allowed' Error?
The "pointer to incomplete class type is not allowed" error occurs when you try to create a pointer to an incomplete class type. For example, if you have the following code:
class MyClass;
MyClass* myClassPtr;
You will get the error message "pointer to incomplete class type is not allowed" because MyClass has been declared but not defined.
How to Fix the 'Pointer to Incomplete Class Type is Not Allowed' Error
To fix the "pointer to incomplete class type is not allowed" error, you need to make sure that the class is defined before you create a pointer to it. You can do this by including the header file that defines the class in the implementation file.
For example, if you have the following code:
// MyClass.h
class MyClass;
// MyClass.cpp
#include "MyClass.h"
MyClass* myClassPtr;
You will get the "pointer to incomplete class type is not allowed" error. To fix this, you need to include the header file that defines MyClass in MyClass.cpp.
// MyClass.h
class MyClass {
public:
void doSomething();
};
// MyClass.cpp
#include "MyClass.h"
void MyClass::doSomething() {
// implementation
}
MyClass* myClassPtr;
Now that MyClass has been defined, you can create a pointer to it without getting the "pointer to incomplete class type is not allowed" error.
FAQ
Q1: What is an incomplete class type?
An incomplete class type is a class that has been declared but not defined.
Q2: Why do I get the "pointer to incomplete class type is not allowed" error?
You get this error when you try to create a pointer to an incomplete class type.
Q3: How do I fix the "pointer to incomplete class type is not allowed" error?
You need to make sure that the class is defined before you create a pointer to it. You can do this by including the header file that defines the class in the implementation file.
Q4: Can I declare a pointer to an incomplete class type?
Yes, you can declare a pointer to an incomplete class type, but you cannot create a pointer to it.
Q5: What is the difference between a declaration and a definition in C++?
A declaration tells the compiler about the existence of a variable, function, or class, while a definition provides the actual implementation of the variable, function, or class.