Run ClangFormat Inside Docker Container on Linux

ClangFormat is a command line tool that automatically formats source code - such as C, C++, Java, JavaScript, Objective-C, and more - based on predefined style guidelines. Having a standardized format improves readability and ensures consistency across the project. By using a Docker container that already has ClangFormat preinstalled, you can run formatting commands in a clean, isolated environment - no system-wide installations needed. It ensures everyone on the team runs the same version of ClangFormat, eliminating inconsistencies caused by tool version differences.

Suppose we have a simple C source file, main.c, that looks like this:

#include <stdio.h>

int main() {
    for(int i=0;i<10;++i){printf("%d\n",i);}

    return 0;
}

To format the code using ClangFormat from a Docker container, run the following command:

docker run -it --rm -v ./:/src -u $(id -u):$(id -g) xianpengshen/clang-tools:20 clang-format -i main.c

Explanation of the command:

• docker run - launches a new Docker container.
• -it - enables interactive mode with a terminal session.
• --rm - automatically removes the container after it finishes running to keep the system tidy.
• -v ./:/src - mounts the current working directory into the container at /src.
• -u $(id -u):$(id -g) - ensures the container runs with the local user permissions.
• xianpengshen/clang-tools - specifies the Docker image to use.
• clang-format -i main.c - runs the formatter on main.c and updates the file in place.

After the command runs, the main.c file will be reformatted in place to follow the default style:

#include <stdio.h>

int main() {
  for (int i = 0; i < 10; ++i) {
    printf("%d\n", i);
  }

  return 0;
}