Скачать или смотреть How to Compile a Header to Executable in CMake

Discover how to compile a dual-purpose header in `CMake` into an executable without manually writing out commands, ensuring a cross-platform approach.
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How to Compile a Header to Executable in CMake

In the world of software development, especially with C+ + , there are scenarios where you might have dual-purpose headers that could be treated as either header files or source files. A common use case is controlling this behavior through preprocessor flags. One such flag is AS_CPP, which allows you to compile a file, like foo.h, directly into an executable. While you can use a simple command line like g+ + -x c+ + -DAS_CPP foo.h -o foo, managing this within a build system like CMake can be tricky. If you've faced challenges in achieving this, you're not alone. Fortunately, there’s a way to tackle this problem seamlessly in CMake, and we’ll guide you through the solution.

The Problem: Compiling Dual-Purpose Headers

When you want to compile a header as if it were a source file in CMake, you may run into an issue where CMake tries to link without properly compiling your header first. This can lead to confusion and errors if you’re dealing with a complex project that requires this functionality.

Your Attempts

You might have tried the following approach and encountered issues:

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This method might make CMake link immediately without recognizing the need to compile the header.

The Solution: Using Custom Commands

To resolve this, we can create a custom command that handles the situation properly. By copying the header to a .cpp file at build time, we can trick CMake into complying with our needs.

Step-by-step Instructions

Here’s a structured approach to implement the solution in your CMake project:

Define a Custom Command: This command will copy your header file to a new file with a .cpp suffix. This way, CMake will treat it as a source file during the build.

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Create the Executable: After defining the copy command, you can now create the executable using the newly copied foo.cpp.

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Why This Works

By copying the header file to a .cpp format, you're allowing CMake to compile it effectively. The add_custom_command ensures that the header copying happens before the build process begins, thus avoiding any linking issues. This method is also cross-platform, fitting nicely within CMake’s intended capabilities.

Conclusion

Compiling a dual-purpose header in CMake doesn't have to be a daunting task. By leveraging custom commands to change the file extension from .h to .cpp, we can ensure a smooth and efficient build process that is also portable across different platforms. This approach not only streamlines the workflow but also helps maintain clarity and organization in your CMake files.

Embrace these techniques, and you'll find yourself better equipped to handle dual-purpose headers in your C+ + projects!