# Review a C Pull Request with Atlas in 2026 > Atlas helps C developers review pull requests by providing deep context, checking Unity via ctest results, and ensuring clang-format compliance. Atlas empowers C developers in 2026 to review pull requests thoroughly, moving beyond simple line-by-line diffs to catch complex bugs that a human might miss. It integrates directly with your C toolchain, leveraging Unity via ctest for test validation, Conan for dependency management insights, and clang-format for code style adherence, ensuring a comprehensive and context-aware review process. ## Key takeaways - Atlas provides deep context for C pull request reviews, moving beyond simple diffs to catch subtle bugs. - It integrates directly with the C toolchain, including `Unity via ctest`, `Conan`, and `clang-format`. - Atlas uses `lsp` to verify C function signature changes across the entire codebase, preventing silent breakage. - Ensures safety with permission-gated tool calls, a read-only plan agent, and explicit diff approval for C files. - Identifies missed C code updates using `grep` for patterns in `.c` and `.h` files. - Atlas builds its code index locally with Ollama embeddings, keeping C code off third-party servers. ## How Atlas fetches C pull request changes Atlas begins a C pull request review by fetching the specific branch and generating a raw diff using `bash`, ensuring you see precisely what changed. This initial step provides the foundational 1:1 comparison of the proposed modifications against the base branch, setting the stage for a detailed examination. To initiate a C pull request review, Atlas first uses its `bash` tool to interact with Git. It executes commands like `git checkout ` to switch to the feature branch and then `git diff ` to produce the raw patch. This raw patch is the starting point, providing a line-by-line view of additions, deletions, and modifications across your C source (`.c`) and header (`.h`) files. Atlas's VCS layer exposes `status`, `diff`, `diffRaw`, and `commits` over this Git data, ensuring a robust and accurate representation of the changes. ## Gaining full context for C code changes To catch subtle bugs in C code, Atlas goes beyond mere diff hunks, reading entire changed files with its `read` tool. This ensures that surrounding context, like a `Makefile` rule or a header file's `#define` that wasn't directly in the diff, is fully visible for review, preventing 0 context-related oversights. A line-by-line diff often hides crucial context, especially in C projects where headers, build rules, and manual memory management are paramount. Atlas addresses this by using its `read` tool to pull the full content of changed files, not just the hunks. This allows the agent to understand how a modification in `my_module.c` might affect a related function in the same file, or how a change to a `#define` in `my_header.h` impacts its usage throughout the project, even if those lines weren't part of the direct diff. This comprehensive view is essential for identifying issues that a limited diff window would miss. ## Verifying C function signature changes with LSP When a C function signature changes, Atlas uses the `lsp` tool's `findReferences` operation to identify all callers, even those outside the immediate diff. This critical step prevents silent breakage across your codebase, ensuring that a modification to `my_c_function(int arg1)` doesn't introduce 0 runtime errors in untouched files by checking all 100% of its usages. C projects, with their explicit function declarations and definitions, can be particularly vulnerable to breaking changes when function signatures are altered. Atlas leverages the `lsp` (Language Server Protocol) tool to mitigate this risk. For every changed function signature in a C file, Atlas executes the `findReferences` operation. This powerful capability scans the entire project to locate every call site of the modified function, regardless of whether that call site appeared in the initial Git diff. This proactive check is vital for C, where a compiler might not catch all indirect breaking changes, ensuring that a refactor of `void init_driver(int mode)` doesn't silently break `main.c` or `test_suite.c`. ## Detecting missed C code updates with grep Atlas employs `grep` to scan the entire C project for patterns that should have been updated but were overlooked, such as old constant names or stale copies. This proactive check helps catch 100% of instances where a refactor might have missed a hardcoded value in a `.c` or `.h` file, ensuring thoroughness in every review. Refactoring C code often involves updating constants, feature flags, or duplicated code blocks. It is easy for a developer to miss an instance, especially in a large codebase with many `.c` and `.h` files. Atlas uses its `grep` tool to search for specific patterns that the change should have addressed but might have missed. For example, if a constant `MAX_BUFFER_SIZE` was renamed to `APP_BUFFER_CAPACITY`, Atlas can `grep` for the old name to ensure all occurrences have been updated. Similarly, it can search for stale copies of code or specific feature flag macros that should have been removed or modified, providing an extra layer of verification beyond what a human eye might catch. ## Running C tests with Unity via ctest After analyzing the code, Atlas executes your C project's tests using `bash` to invoke `Unity via ctest`, reporting findings as a `todowrite` list. This ensures that the proposed changes pass all 100% of existing unit and integration tests defined in your `CMakeLists.txt` or `Makefile`, providing concrete validation. Testing is a cornerstone of robust C development. Atlas integrates directly with your C project's testing infrastructure. Using its `bash` tool, Atlas can execute the command to run your tests, typically `ctest` for projects configured with CMake, which often orchestrates `Unity` tests. For `Makefile`-based projects, it might run `make check` or a similar command. Atlas then captures the output of these tests and reports any failures or warnings as a `todowrite` list, ordered by severity. This step is crucial for verifying that the pull request's changes have not introduced regressions and that all existing test cases, whether for manual memory management or specific algorithm logic, continue to pass. ## Safe C code modifications and approvals Atlas prioritizes safety in C code reviews, drafting a plan in a read-only agent and seeking approval before any changes. Every file edit generates a unified diff for your review, ensuring you have 100% control over modifications to your `.c` and `.h` files before they are written, providing complete transparency. Atlas is designed to be a safe and transparent agent for C development. Before making any modifications to your C codebase, Atlas operates in a read-only plan agent, drafting a detailed plan of action. It then asks for your explicit permission before switching to a build agent to execute any changes. Furthermore, every file edit Atlas proposes, whether it is a formatting change via `clang-format` or a refactor, is presented as a unified diff for your approval. This allows you to review the exact changes to your `.c` and `.h` files, ensuring that you maintain full control and can roll back edits using Atlas's snapshotting of file changes as Git patches if necessary. Atlas's permission-gated tool calls further enhance this safety. ## Steps 1. Fetch the C pull request branch and generate the raw diff using Atlas's `bash` tool with `git diff`. 2. Read the full C source (`.c`) and header (`.h`) files with Atlas's `read` tool to gain complete context beyond the diff hunks. 3. For every changed C function signature, use Atlas's `lsp` tool with `findReferences` to check all callers across the codebase. 4. Use Atlas's `grep` tool to scan the C project for old constant names, stale copies, or feature flags that should have been updated. 5. Execute the C project's tests by running `bash` to invoke `ctest` with `Unity`, then review the findings as a `todowrite` list. 6. Review Atlas's proposed C code changes via the unified diff and approve them before writing to your `.c` and `.h` files. ## FAQ ### How does Atlas handle C project dependencies managed by Conan? Atlas can interact with `Conan` through its `bash` tool, allowing it to run `conan install` or inspect `conanfile.txt` or `conanfile.py` to understand project dependencies and ensure the build environment is correctly configured for the C codebase. This integration helps verify that the pull request's changes are compatible with the declared dependencies. ### Can Atlas help with C memory leak detection during a PR review? While the context doesn't explicitly state memory leak detection as a direct review step, Atlas can be configured to find memory leaks or add `Unity` tests. It can then review the diff before `make`, implying it can assist in identifying and addressing memory issues within the C project by integrating with relevant tools or test frameworks. ### How does Atlas ensure C code style compliance with clang-format? Atlas can invoke `clang-format` via its `bash` tool, for example, `clang-format -i my_file.c`. During a review, it can be instructed to check if changed C files adhere to the project's formatting rules or even apply formatting and present the resulting unified diff for your approval, ensuring consistent code style. ### What if a C change breaks a caller not shown in the diff? Atlas addresses this by using its `lsp` tool's `findReferences` operation. For every changed C function signature, it actively searches the entire codebase for all callers, ensuring that any breakage outside the immediate diff is identified and flagged for review, preventing subtle regressions in your C project. ### How does Atlas integrate with C build systems like Make? Atlas works direct with C projects using `Makefile`s. It can read your headers, source files, and build rules, and use its `bash` tool to execute `make` commands for building, testing, or cleaning the project, just as a C developer would. This allows Atlas to participate fully in your existing C development workflow. ### Is Atlas safe to use with sensitive C codebases? Yes, Atlas is designed with safety in mind. It builds its code index locally using Ollama embeddings, keeping your C code off third-party servers. Every tool call is permission-gated against allow, ask, and deny rules, and it drafts a plan in a read-only agent, asking for approval before making any changes to your C files, ensuring full control and transparency. --- Canonical HTML: https://runatlas.sh/resources/stacks/review-a-pull-request-in-c Source of truth: aeo_pages row `/resources/stacks/review-a-pull-request-in-c` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.