C

C Project Rules

Agent Automation Commands

CRITICAL: Execute these commands after EVERY implementation (see AGENT_AUTOMATION module for full workflow).

# Complete quality check sequence:
clang-format --dry-run --Werror src/**/*.c  # Format check
make lint                 # Linting (if configured)
make test                 # All tests (100% pass)
make                      # Build verification

# Memory safety (recommended):
valgrind --leak-check=full ./build/test  # Memory leak check

C Configuration

CRITICAL: Use C11 or C17 standard with strict warnings enabled.

• Standard: C11 or C17
• Compiler: GCC 11+ or Clang 14+
• Build System: CMake 3.20+ (recommended) or Make
• Warnings: Treat all warnings as errors
• Sanitizers: ASAN, UBSAN for memory safety

CMakeLists.txt Requirements

cmake_minimum_required(VERSION 3.20)
project(YourProject C)

set(CMAKE_C_STANDARD 17)
set(CMAKE_C_STANDARD_REQUIRED ON)
set(CMAKE_C_EXTENSIONS OFF)

# Compiler warnings
if(MSVC)
  add_compile_options(/W4 /WX)
else()
  add_compile_options(-Wall -Wextra -Werror -pedantic)
endif()

# Enable sanitizers in Debug mode
if(CMAKE_BUILD_TYPE STREQUAL "Debug")
  add_compile_options(-fsanitize=address,undefined)
  add_link_options(-fsanitize=address,undefined)
endif()

# Source files
add_executable(${PROJECT_NAME} src/main.c src/module.c)

# Include directories
target_include_directories(${PROJECT_NAME} PUBLIC include)

# Enable testing
enable_testing()
add_subdirectory(tests)

Code Quality Standards

Mandatory Quality Checks

CRITICAL: After implementing ANY feature, you MUST run these commands in order.

IMPORTANT: These commands MUST match your GitHub Actions workflows to prevent CI/CD failures!

# Pre-Commit Checklist (MUST match .github/workflows/*.yml)

# 1. Format check (matches workflow - use --dry-run, not -i!)
clang-format --dry-run --Werror src/**/*.c include/**/*.h tests/**/*.c

# 2. Static analysis (matches workflow)
clang-tidy src/**/*.c -- -std=c17 -Wall -Wextra -Werror

# 3. Build with warnings as errors (matches workflow)
cmake -B build -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS="-Werror -Wall -Wextra -pedantic"
cmake --build build

# 4. Run all tests (MUST pass 100% - matches workflow)
ctest --test-dir build --output-on-failure --verbose

# 5. Check with Address Sanitizer (matches workflow)
cmake -B build-asan -DCMAKE_BUILD_TYPE=Debug \
  -DCMAKE_C_FLAGS="-fsanitize=address,undefined -g"
cmake --build build-asan
ctest --test-dir build-asan --output-on-failure

# 6. Check with Valgrind (matches workflow)
valgrind --leak-check=full --error-exitcode=1 ./build/YourProject

# 7. Check coverage (matches workflow)
cmake -B build-cov -DCMAKE_BUILD_TYPE=Coverage \
  -DCMAKE_C_FLAGS="-fprofile-arcs -ftest-coverage"
cmake --build build-cov
ctest --test-dir build-cov
gcov build-cov/CMakeFiles/YourProject.dir/src/*.gcno
lcov --capture --directory build-cov --output-file coverage.info
lcov --list coverage.info

# If ANY fails: ❌ DO NOT COMMIT - Fix first!

If ANY of these fail, you MUST fix the issues before committing.

Why This Matters:

• Running different commands locally than in CI causes "works on my machine" failures
• CI/CD failures happen when local checks differ from workflows
• Example: Using clang-format -i locally but --dry-run --Werror in CI = failure
• Example: Missing -Werror flag = warnings pass locally but fail in CI
• Example: Skipping sanitizers locally = CI catches memory bugs, use-after-free, buffer overflows
• Example: Not running Valgrind = memory leaks pass locally but fail in CI

Formatting

• Use clang-format for consistent code style
• Configuration in .clang-format
• Check formatting in CI (don't auto-format)

Example .clang-format:

Language: C
BasedOnStyle: LLVM
IndentWidth: 4
ColumnLimit: 100
AllowShortFunctionsOnASingleLine: Empty
BreakBeforeBraces: Attach
AlignConsecutiveMacros: true

Static Analysis

• Use clang-tidy for static analysis
• Configuration in .clang-tidy
• Enable modernize and bugprone checks

Example .clang-tidy:

Checks: >
  -*,
  bugprone-*,
  clang-analyzer-*,
  modernize-*,
  readability-*,
  performance-*,
  portability-*

CheckOptions:
  - key: readability-identifier-naming.FunctionCase
    value: lower_case
  - key: readability-identifier-naming.VariableCase
    value: lower_case

Testing

• Framework: Unity, Check, or CTest
• Location: /tests directory
• Coverage: Must meet threshold (80%+)
• Sanitizers: ASAN, UBSAN, Valgrind
• Memory Safety: Zero memory leaks

Example Unity test:

#include "unity.h"
#include "module.h"

void setUp(void) {
    // Setup before each test
}

void tearDown(void) {
    // Cleanup after each test
}

void test_function_should_return_expected_value(void) {
    int result = my_function(10);
    TEST_ASSERT_EQUAL_INT(20, result);
}

void test_function_should_handle_null_pointer(void) {
    TEST_ASSERT_NULL(my_function_with_null(NULL));
}

int main(void) {
    UNITY_BEGIN();
    RUN_TEST(test_function_should_return_expected_value);
    RUN_TEST(test_function_should_handle_null_pointer);
    return UNITY_END();
}

Memory Safety

CRITICAL: Always check for memory issues.

Required Checks

1. Address Sanitizer (ASAN):

   gcc -fsanitize=address -g -o program main.c
   ./program
   

2. Undefined Behavior Sanitizer (UBSAN):

   gcc -fsanitize=undefined -g -o program main.c
   ./program
   

3. Valgrind:

   valgrind --leak-check=full --show-leak-kinds=all ./program
   

4. Static Analysis:

   clang-tidy src/**/*.c
   cppcheck --enable=all --error-exitcode=1 src/
   

Common Memory Issues to Prevent

// ❌ BAD: Memory leak
char *buffer = malloc(100);
// ... use buffer ...
// Missing free()

// ✅ GOOD: Proper cleanup
char *buffer = malloc(100);
if (buffer == NULL) {
    return ERROR_NO_MEMORY;
}
// ... use buffer ...
free(buffer);
buffer = NULL;

// ❌ BAD: Use after free
char *ptr = malloc(10);
free(ptr);
strcpy(ptr, "test");  // UNDEFINED BEHAVIOR!

// ✅ GOOD: NULL after free
char *ptr = malloc(10);
free(ptr);
ptr = NULL;
if (ptr != NULL) {
    strcpy(ptr, "test");
}

// ❌ BAD: Buffer overflow
char buffer[10];
strcpy(buffer, "This is too long");  // BUFFER OVERFLOW!

// ✅ GOOD: Bounds checking
char buffer[10];
strncpy(buffer, "Safe", sizeof(buffer) - 1);
buffer[sizeof(buffer) - 1] = '\0';

Best Practices

DO's ✅

• CHECK return values from all functions
• VALIDATE all pointer arguments for NULL
• FREE all allocated memory
• USE const for immutable pointers
• LIMIT variable scope
• ZERO memory after free for security
• BOUNDS check all array accesses
• SANITIZE all inputs

DON'Ts ❌

• NEVER ignore compiler warnings
• NEVER assume malloc succeeds
• NEVER use gets() (use fgets())
• NEVER use strcpy() (use strncpy() or strlcpy())
• NEVER use sprintf() (use snprintf())
• NEVER dereference NULL pointers
• NEVER return pointers to stack variables
• NEVER skip sanitizer checks

Security Guidelines

1. Input Validation: Validate all external inputs
2. Buffer Safety: Always check bounds
3. Integer Overflow: Check arithmetic operations
4. Format String: Never use user input as format string
5. Memory Zeroization: Zero sensitive data after use

Example secure code:

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

// Secure string copy with bounds checking
int safe_strcpy(char *dest, size_t dest_size, const char *src) {
    if (dest == NULL || src == NULL || dest_size == 0) {
        return -1;
    }
    
    size_t src_len = strlen(src);
    if (src_len >= dest_size) {
        return -1;  // Not enough space
    }
    
    strncpy(dest, src, dest_size - 1);
    dest[dest_size - 1] = '\0';
    return 0;
}

// Secure memory cleanup
void secure_free(void **ptr, size_t size) {
    if (ptr == NULL || *ptr == NULL) {
        return;
    }
    
    // Zero memory before free
    memset(*ptr, 0, size);
    free(*ptr);
    *ptr = NULL;
}