Keep Track of Commit id in Code Development

Obtaining the current Git commit ID in C++ code serves several purposes, mainly for debugging, version tracking, and reproducibility.

1. Importance

Here are some common reasons.

1.1 Version Identification

1. Embedding the commit ID allows you to track exactly which version of the code was used in a given build.
2. Useful in applications where users report issues, so developers can quickly identify the codebase version.

1.2 Reproducibility and Debugging

1. When debugging issues, knowing the exact commit helps developers check out the same version and reproduce bugs.
2. If a crash report or log includes the commit ID, developers can match it to the corresponding source code.

1.3 CI/CD

1. Including the commit ID in the build helps with tracking which commit was deployed.
2. This is essential in automated deployment pipelines.

2. The Most Common Practice

We can embed the commit ID into the C++ program at compile time by using git rev-parse --short HEAD. We can achieve that by adding the following to our CMakeLists.txt to extract the Git commit ID and define it as a macro.

# Get the current Git commit ID
execute_process(
    COMMAND git rev-parse --short HEAD
    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
    OUTPUT_VARIABLE GIT_COMMIT_ID
    OUTPUT_STRIP_TRAILING_WHITESPACE
)

# Define the commit ID as a preprocessor macro
add_definitions(-DGIT_COMMIT_ID="${GIT_COMMIT_ID}")

And then we can use the macro in C++ code.

#include <iostream>

#ifndef GIT_COMMIT_ID
#define GIT_COMMIT_ID "unknown"
#endif

int main() {
    std::cout << "Current Git Commit ID: " << GIT_COMMIT_ID << std::endl;
    return 0;
}

Here is the complete CMakeLists.txt file.

# Minimum CMake version required
cmake_minimum_required(VERSION 3.10)

# Project name
project(GitCommitExample VERSION 1.0)

# Set C++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

# Get the current Git commit ID
execute_process(
    COMMAND git rev-parse --short HEAD
    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
    OUTPUT_VARIABLE GIT_COMMIT_ID
    OUTPUT_STRIP_TRAILING_WHITESPACE
    RESULT_VARIABLE GIT_RESULT
)

# Check if the git command succeeded, otherwise set a fallback value
if(NOT GIT_RESULT EQUAL 0)
    set(GIT_COMMIT_ID "unknown")
endif()

# Define the commit ID as a preprocessor macro
add_definitions(-DGIT_COMMIT_ID="${GIT_COMMIT_ID}")

# Add the executable
add_executable(main main.cpp)