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c_pitfalls.md
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Unless specified otherwise, this article supposes the C99 standard of the C language.
**Generally**: be sure to check your programs with tools such as [valgrind](valgrind.md), [splint](splint.md) or [cppcheck](cppcheck.md), and turn on compiler auto checks (`-Wall`, `-Wextra`, `-pedantic`, ...), it's quick, simple and reveals many bugs!
**Generally**: be sure to check your programs with tools such as [valgrind](valgrind.md), [splint](splint.md), [cppcheck](cppcheck.md), UBSan or ASan, and turn on compiler auto checks (`-Wall`, `-Wextra`, `-pedantic`, ...), it's quick, simple and reveals many bugs!
## Undefined/Unspecified Behavior
Undefined (completely unpredictable), unspecified (safe but potentially differing) and implementation-defined (consistent within implementation but potentially differing between them) behavior poses a kind of unpredictability and sometimes non-intuitive, tricky behavior of certain operations that may differ between compilers, platforms or runs because they are not exactly described by the language specification; this is mostly done on purpose so as to allow some implementation freedom which allows implementing the language in a way that is most efficient on given platform. One has to be very careful about not letting such behavior break the program on platforms different from the one the program is developed on. Note that tools such as [cppcheck](cppcheck.md) can help find undefined behavior in code. Description of some such behavior follows.
There are tools for detecting undefined behavior, see e.g. [clang](clang.md)'s UBSan (https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html).
**Data type sizes including int and char may not be the same on each platform**. Even though we almost take it for granted that char is 8 bits wide, in theory it can be different (even though `sizeof(char)` is always 1). Int (and unsigned int) type width should reflect the architecture's native integer type, so nowadays it's mostly 32 or 64 bits. To deal with these differences we can use the standard library `limits.h` and `stdint.h` headers.
**No specific [endianness](endian.md) or even encoding of numbers is specified**. Nowadays little endian and [two's complement](twos_complement.md) is what you'll encounter on most platforms, but e.g. [PowerPC](ppc.md) uses big endian ordering.