How to use the command clang-format (with examples)

Clang-format is a powerful tool used for auto-formatting code written in C, C++, Java, JavaScript, Objective-C, Protobuf, and C#. It helps developers follow consistent coding styles and improves code readability. This article will provide examples of different use cases of the clang-format command.

Use case 1: Format a file and print the result to stdout

Code:

clang-format path/to/file

Motivation:

This use case is useful when you want to see how the code will be formatted without modifying the actual file. It allows you to preview the changes before applying them.

Explanation:

• clang-format: The command to invoke the clang-format tool.
• path/to/file: The path to the file you want to format.

Example output:

The code from the file will be displayed in the terminal with the formatted result.

Use case 2: Format a file in-place

Code:

clang-format -i path/to/file

Motivation:

This use case is beneficial when you want to modify the file with the desired formatting without creating a separate file. It makes it easier to apply changes to large codebases quickly.

Explanation:

• clang-format: The command to invoke the clang-format tool.
• -i: The option to enable in-place formatting.
• path/to/file: The path to the file you want to format.

Example output:

The file specified will be modified, and the changes will be applied directly to the file.

Use case 3: Format a file using a predefined coding style

Code:

clang-format --style=LLVM|GNU|Google|Chromium|Microsoft|Mozilla|WebKit path/to/file

Motivation:

This use case is ideal when you want to format the code according to a specific coding style standard. Clang-format supports various predefined coding styles, allowing you to easily adhere to the standards followed by different organizations and communities.

Explanation:

• clang-format: The command to invoke the clang-format tool.
• --style: The option to specify the coding style to be used for formatting. You can choose from LLVM, GNU, Google, Chromium, Microsoft, Mozilla, or WebKit.
• path/to/file: The path to the file you want to format.

Example output:

The code will be formatted according to the selected coding style, and the result will be displayed in the terminal.

Use case 4: Format a file using the .clang-format file in one of the parent directories of the source file

Code:

clang-format --style=file path/to/file

Motivation:

This use case is helpful when you want to use the coding style defined in the .clang-format file located in one of the parent directories of the source file. It allows for using a custom coding style configuration for the specific project.

Explanation:

• clang-format: The command to invoke the clang-format tool.
• --style=file: The option to use the .clang-format file located in the parent directories for formatting.
• path/to/file: The path to the file you want to format.

Example output:

The code will be formatted based on the rules specified in the .clang-format file, and the result will be displayed in the terminal.

Use case 5: Generate a custom .clang-format file

Code:

clang-format --style=LLVM|GNU|Google|Chromium|Microsoft|Mozilla|WebKit --dump-config > .clang-format

Motivation:

This use case is useful when you want to generate a custom .clang-format file based on one of the predefined coding styles provided by clang-format. It allows you to create a configuration file that can be further customized as per your project’s requirements.

Explanation:

• clang-format: The command to invoke the clang-format tool.
• --style: The option to specify the coding style to be used for generating the configuration file.
• --dump-config: The option to generate a configuration file.
• >: Redirects the output to a file.
• .clang-format: The file name of the custom configuration file being created.

Example output:

A .clang-format file will be generated in the current directory, containing the configuration options for the chosen coding style. You can further modify this file to customize the formatting rules according to your project’s needs.

Conclusion:

Clang-format is a versatile command-line tool that simplifies the task of formatting code written in various programming languages. By understanding and utilizing the different use cases described above, developers can easily apply consistent code formatting and improve code readability, leading to more maintainable codebases.