Expression Must Be a Pointer to a Complete Object Type
I remember the first time I tried to code in C++. I was so excited to finally be able to create my own programs, but I quickly ran into a problem. I kept getting errors about expressions that had to be pointers to complete object types. I didn’t understand what this meant, and it took me a while to figure it out..
As I learned, an expression is a combination of variables, constants, and operators that evaluates to a single value. In C++, an expression must be a pointer to a complete object type if it is used in certain contexts, such as when it is passed as an argument to a function or returned from a function.
What is a Pointer?
A pointer is a variable that stores the address of another variable. This allows you to indirectly access the value of the other variable.
In C++, pointers are declared using the asterisk (*) operator. For example, the following code declares a pointer to an integer:
int *ptr;What is a Complete Object Type?
A complete object type is a type that has been fully defined. This means that the compiler knows the size and layout of the object.
In C++, there are two types of object types: complete object types and incomplete object types. A complete object type is a type that has been defined with a struct, union, or class. An incomplete object type is a type that has been declared but not defined.
Why Must Expressions Be Pointers to Complete Object Types?
There are two reasons why expressions must be pointers to complete object types.
- To ensure that the compiler knows the size and layout of the object. This is important because the compiler needs to know how much memory to allocate for the object and how to access its members.
- To prevent dangling pointers. A dangling pointer is a pointer that points to an object that has been deleted. Dangling pointers can cause errors if they are used.
How to Avoid Errors with Expressions That Must Be Pointers to Complete Object Types
There are a few things you can do to avoid errors with expressions that must be pointers to complete object types.
- Always declare pointers to complete object types. This will ensure that the compiler knows the size and layout of the object.
- Never use dangling pointers. If you are finished with an object, delete it to prevent it from becoming a dangling pointer.
Conclusion
Expressions that must be pointers to complete object types are an important part of C++. By understanding the rules for using pointers, you can avoid errors and write code that is safe and efficient.
Are you interested in learning more about C++? If so, I encourage you to check out the following resources:
- The C++ Programming Language by Bjarne Stroustrup
- The C++ Standard Library by Nicolai Josuttis
- The C++ FAQ Lite
FAQs
- What is an expression?
- An expression is a combination of variables, constants, and operators that evaluates to a single value.
- What is a pointer?
- A pointer is a variable that stores the address of another variable.
- What is a complete object type?
- A complete object type is a type that has been fully defined.
- Why must expressions be pointers to complete object types?
- There are two reasons why expressions must be pointers to complete object types: to ensure that the compiler knows the size and layout of the object, and to prevent dangling pointers.
- How can I avoid errors with expressions that must be pointers to complete object types?
- There are two things you can do to avoid errors with expressions that must be pointers to complete object types: always declare pointers to complete object types, and never use dangling pointers.
