• Do not use identifiers that are already declared
  • For example, don't name a variable errno
• Do not pass functions invalid values
• For floating point exception functions, only pass 0 or bitwise OR of floating point macros
• Do not modify the string returned by setlocale()
• Do not call setjmp() in stupid places (eg. header files)
• Do not call longjmp() before calling setjmp()
• Do not call va_start() with a parameter declared with the register storage class, of array type, or a type that isn't compatible with the type after default argument promotions
• Do not try to get the address constant of a bit-field
  • For example, do not: &(t.member-designator)
• When functions fail, data structures often have indeterminate contents
  • eg. wcsxfrm(), wcsftime(), mbrtowc(), wcrtomb()
• Do not mismatch multibyte conversion states with character sequences in another state
• Only pass functions the type they ask for
  • We might already have a rule for this, but I couldn't find it