What are C++ Modules?

Traditionally, C++ code is organized into header files (.h) and source files (.cpp). When a C++ program is compiled, the compiler must process each header file individually, resulting in redundant and time-consuming compilation steps.

C++ Modules aim to solve this problem by introducing a new module system. A module is a self-contained unit of code that encapsulates definitions and declarations, much like a header file. However, unlike header files, modules are compiled only once and are not subject to redundant inclusion.

Declaring a Module

To declare a module, we use the module keyword followed by the name of the module. For example, to declare a module named MyModule, we would write:

module MyModule;

This declaration should be placed at the beginning of the module file, which has the extension .cppm.

Exporting Definitions

Inside a module, we can define classes, functions, variables, and other entities just like in a regular source file. However, to make these definitions accessible outside the module, we need to use the export keyword.

For example, let’s say we have a class named MyClass that we want to export:

// MyModule.cppm
module MyModule;

export class MyClass {
    // Class definition...
};

With the export keyword, the MyClass is now accessible to other modules and files that import the MyModule.

Importing a Module

To use a module, we need to import it into our source file. This is done using the import keyword, followed by the name of the module.

// main.cpp
import MyModule;

int main() {
    // Code using definitions from MyModule...
    return 0;
}

Once imported, we can access the exported entities from the module as if they were declared locally.

Building and Using Modules

To compile C++ code with modules, we need a compiler that supports C++20. Most modern compilers, like GCC and Clang, have added support for C++ Modules.

To compile a module file, we use the compiler flag -std=c++20 along with the .cppm file:

$ g++ -std=c++20 MyModule.cppm -o MyModule

Once compiled, we can use the module by importing it into any source file and compiling it using the same flag:

$ g++ -std=c++20 main.cpp -o main

By using C++ Modules, we can improve compilation times by reducing redundancy and recompilation. Additionally, modules provide a cleaner and more organized code structure, making the development process more efficient and maintainable.

Conclusion

C++ Modules bring a revolutionary change to how we organize and manage code in C++. By reducing redundancy, improving compilation times, and enhancing code maintainability, modules prove to be a valuable addition to the C++ language. Incorporating modules into your C++ projects can significantly enhance the development process and improve coding efficiency.

#C++ #Modules