include guard c++

An include guard in C++ is used to prevent multiple inclusion of the same header file in a program. It ensures that the contents of the header file are only included once, even if the file is included multiple times in different parts of the codebase. Here are the steps to create an include guard in C++:

  1. Begin by opening the header file that you want to protect with an include guard.

  2. At the top of the file, before any other code, add the following lines:

#ifndef FILENAME_H
#define FILENAME_H

Replace "FILENAME_H" with a unique identifier for your file. It is common practice to use the name of the file in uppercase with an underscore (_) as a separator. This identifier acts as a macro that will be defined only if it has not been defined before.

  1. Next, add all the content of your header file after the include guard, including any declarations, definitions, and preprocessor directives.

  2. Finally, add the following line at the end of the file:

#endif // FILENAME_H

This line closes the include guard section.

By using an include guard, you ensure that when the header file is included for the first time, the macro "FILENAME_H" is defined, preventing subsequent inclusion of the same file. This avoids compiler errors that can occur due to redefinition of classes, functions, or variables.

The include guard mechanism is essential in large codebases where header files may be included by multiple source files, preventing duplicate definitions and improving compilation time.