C

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name: C slug: c version: 1.0.1 description: Write safe C avoiding memory corruption, buffer overflows, and undefined behavior traps. homepage: https://clawic.com/skills/c metadata: clawdbot: emoji: ⚙️ requires: bins: - gcc - clang os: - linux - darwin - win32 displayName: C

Quick Reference

Topic	File
malloc/free, leaks, double free	memory.md
Null, dangling, pointer arithmetic	pointers.md
Null terminator, buffer overflow	strings.md
Integer overflow, signed/unsigned	types.md
Macro traps, include guards	preprocessor.md
Common undefined behavior	undefined.md

Critical Rules

• malloc returns void* — cast required in C++, optional in C but check for NULL
• free(ptr); ptr = NULL; — always null after free to prevent double-free
• sizeof(array) in function gives pointer size, not array size — pass length separately
• char str[5] = "hello"; — no room for null terminator, UB when used as string
• strcpy doesn't check bounds — use strncpy and manually null-terminate
• Signed overflow is UB — compiler can optimize assuming it never happens
• i++ + i++ is UB — no sequence point between modifications
• Returning pointer to local variable — dangling pointer, UB on use
• #define SQUARE(x) x*x — SQUARE(1+2) = 1+2*1+2 = 5, not 9
• memcpy with overlapping regions — use memmove instead
• Uninitialized variables — contain garbage, UB if used
• Array out of bounds — no runtime check, silent corruption or crash