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// Write safe C avoiding memory corruption, buffer overflows, and undefined behavior traps.

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updated:March 4, 2026
SKILL.mdreadonly
SKILL.md Frontmatter
nameC
slugc
version1.0.1
descriptionWrite safe C avoiding memory corruption, buffer overflows, and undefined behavior traps.
metadata[object Object]

Quick Reference

TopicFile
malloc/free, leaks, double freememory.md
Null, dangling, pointer arithmeticpointers.md
Null terminator, buffer overflowstrings.md
Integer overflow, signed/unsignedtypes.md
Macro traps, include guardspreprocessor.md
Common undefined behaviorundefined.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