c

C: Idiomatic Efficiency Reference

When to Use

• Use this skill when the task matches this description: Language-specific super-code guidelines for c.

Table of Contents

1. [Memory Management](#memory)
2. [Pointers & Arrays](#pointers)
3. [Error Handling](#errors)
4. [Strings](#strings)
5. [Structs & Enums](#structs)
6. [Preprocessor & Headers](#preprocessor)
7. [Anti-patterns specific to C](#antipatterns)

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1. Memory Management {#memory}

// ❌ malloc without checking return value
char *buf = malloc(size);
strcpy(buf, src);

// ✅
char *buf = malloc(size);
if (!buf) return -ENOMEM;
memcpy(buf, src, size);

// ❌ Casting malloc result (unnecessary in C, hides missing #include)
int *p = (int *)malloc(n * sizeof(int));

// ✅
int *p = malloc(n * sizeof *p);

// ❌ free without nulling (dangling pointer risk in long-lived scope)
free(ptr);
// ... later code might use ptr

// ✅
free(ptr);
ptr = NULL;

// ❌ Forgetting to free on early-return paths
char *a = malloc(100);
char *b = malloc(200);
if (!b) return -1; // leaks a

// ✅ — single cleanup label
char *a = NULL, *b = NULL;
a = malloc(100);
if (!a) goto cleanup;
b = malloc(200);
if (!b) goto cleanup;
// ... use a, b ...
cleanup:
    free(b);
    free(a);

**Use sizeof ptr instead of sizeof(Type) — it stays correct when the type changes.*

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2. Pointers & Arrays {#pointers}