C Development

Write safe, efficient C code for systems programming.

When to use

Writing C code
Memory management issues
System programming
Embedded systems
Performance-critical code

Memory management

Allocation patterns

// Always check malloc
void* ptr = malloc(size);
if (ptr == NULL) {
    fprintf(stderr, "malloc failed\n");
    return -1;
}

// Pair malloc with free
char* buffer = malloc(1024);
// ... use buffer ...
free(buffer);
buffer = NULL;  // Prevent use-after-free

// Use calloc for zero-initialized memory
int* array = calloc(count, sizeof(int));

// Realloc safely
void* new_ptr = realloc(ptr, new_size);
if (new_ptr == NULL) {
    free(ptr);  // Original still valid on failure
    return -1;
}
ptr = new_ptr;

Common patterns

// RAII-style cleanup with goto
int process_file(const char* path) {
    int result = -1;
    FILE* fp = NULL;
    char* buffer = NULL;

    fp = fopen(path, "r");
    if (!fp) goto cleanup;

    buffer = malloc(1024);
    if (!buffer) goto cleanup;

    // ... process ...
    result = 0;

cleanup:
    free(buffer);
    if (fp) fclose(fp);
    return result;
}

Data structures

// Linked list node
typedef struct Node {
    void* data;
    struct Node* next;
} Node;

// Dynamic array
typedef struct {
    void** items;
    size_t count;
    size_t capacity;
} DynArray;

int dynarray_push(DynArray* arr, void* item) {
    if (arr->count >= arr->capacity) {
        size_t new_cap = arr->capacity ? arr->capacity * 2 : 8;
        void** new_items = realloc(arr->items, new_cap * sizeof(void*));
        if (!new_items) return -1;
        arr->items = new_items;
        arr->capacity = new_cap;
    }
    arr->items[arr->count++] = item;
    return 0;
}

Error handling

// Check all system calls
int fd = open(path, O_RDONLY);
if (fd == -1) {
    perror("open");
    return -1;
}

ssize_t n = read(fd, buf, sizeof(buf));
if (n == -1) {
    perror("read");
    close(fd);
    return -1;
}

Debugging

# Compile with debug symbols
gcc -g -Wall -Wextra -Werror -o prog prog.c

# Run with valgrind
valgrind --leak-check=full ./prog

# GDB debugging
gdb ./prog
(gdb) break main
(gdb) run
(gdb) print variable
(gdb) backtrace

Best practices

Check all return values
Initialize all variables
Use const where possible
Prefer stack over heap when size is known
Use -Wall -Wextra -Werror flags

Examples

Input: "Fix memory leak" Action: Run valgrind, trace allocation, ensure every malloc has free

Input: "Optimize this C code" Action: Profile with perf, identify hotspots, optimize critical path

c-lang