About the reasons and solutions for the .cpp file to contain another .cpp file error

About the reasons and solutions for the .cpp file to contain another .cpp file error

In C++ programming, we often encounter situations where we need to include one .cpp file into another .cpp file. However, sometimes we may encounter compilation errors or linking errors that prevent the program from building smoothly. This article explores the causes of this error and offers some solutions.

1. The reason for the error:

1. Repeated inclusion of header files: When the same header file is repeatedly included in multiple .cpp files, it will cause a redefinition error. This is because the function or variable in the header file is defined repeatedly.

2. Dependency errors: If a .cpp file depends on some functions or variables in another .cpp file, but the corresponding header file is not included correctly, it will result in a symbol not found link error.

Second, the solution:

1. Protect macros with header files: Add preprocessing directives at the beginning and end of each header file to avoid repeated inclusion. For example, add the following code to the header file:

   #ifndef HEADER_NAME_H
   #define HEADER_NAME_H
   
   // 头文件内容
   
   #endif
   

2. Use a forward declaration: If a .cpp file only needs to use the declaration of a class in another .cpp file but not its definition, you can use a forward declaration instead of including the entire header file. For example, add a forward declaration of the class in the .cpp file that needs to be used:

   class ClassName; // 前置声明
   
   // 使用ClassName的代码
   

3. Check dependencies: Make sure each .cpp file includes the header files it depends on. If you get a symbol not found link error, check for missing includes of some header files.

4. Realize separate compilation: put the implementation code and declaration code of the program in the .cpp file and the header file respectively, and then compile the .cpp file into the target file