Makefiles are widely used in the C++ development process to automate the building and compiling of code. One common requirement in C++ development is the need for code generation, such as for generating source files, header files, or even build configuration files.

In this blog post, we will discuss how to integrate C++ code generation into your Makefile, allowing you to generate code as part of the build process.

Why Code Generation in C++?

Code generation in C++ can be beneficial in various scenarios. Some common use cases include:

• Creating boilerplate code or repetitive code snippets
• Generating serialization/deserialization functions
• Creating build configurations or project files for different platforms
• Automatic stub generation for testing or interface implementation

By automating code generation, you can save time and ensure consistency across your codebase.

Generating Code with Makefile Rules

Let’s assume that we want to generate a header file from a template to include in our C++ project. We can accomplish this by adding a rule to our Makefile.

generated_header: template_file.txt
    @echo "Generating header file"
    @cat template_file.txt > generated_header.h

In this example, we have a target named generated_header that depends on the template_file.txt. When we run make generated_header, it will check if template_file.txt has been modified since the last build, and if so, it will execute the rule.

In the rule, we perform the necessary actions to generate the header file, which in this case involves copying the contents of template_file.txt to generated_header.h.

To incorporate code generation into the overall build process, you can include this rule as a dependency for your main build target:

CPP_FILES = main.cpp generated_header.h

my_program: $(CPP_FILES)
    g++ $(CPP_FILES) -o my_program

By including generated_header.h as a dependency in the build target, it ensures that the header file is generated before the build starts.

Automating Code Generation with Scripting Languages

While simple code generation can be achieved directly in the Makefile, more complex scenarios often require the use of scripting languages like Python, Ruby, or Bash. These languages provide more advanced functionalities for generating code.

Consider the following example using Python:

generated_cpp_files: generate_code.py
    @echo "Generating C++ files"
    @python generate_code.py

In this case, we have a rule that depends on the generate_code.py script. When executed, the script will generate the necessary C++ files.

You can combine this rule with your main build target by incorporating generated_cpp_files as a dependency:

generated_cpp_files := $(shell make -s generated_cpp_files)

my_program: $(generated_cpp_files) main.cpp
    g++ $(generated_cpp_files) main.cpp -o my_program

Here, we use the $(shell make -s generated_cpp_files) syntax to capture the output of the generated_cpp_files target, which runs the code generation script. This ensures that the script is executed before building the target my_program.

Conclusion

Integrating code generation into your Makefile allows you to automate the process of generating C++ code, saving time and ensuring consistency. By properly defining dependencies and rules, you can incorporate code generation seamlessly into your build process.

Using simple rules or leveraging scripting languages, you can generate various artifacts like source files, header files, or even build configurations, tailored to your specific needs.

With code generation as part of your workflow, you can enhance your C++ development process by minimizing repetitive tasks and maintaining a more maintainable and efficient codebase.