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