path: root/include/stddef.h
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2014-08-20add max_align_t definition for C11 and C++11Rich Felker-0/+3
unfortunately this needs to be able to vary by arch, because of a huge mess GCC made: the GCC definition, which became the ABI, depends on quirks in GCC's definition of __alignof__, which does not match the formal alignment of the type. GCC's __alignof__ unexpectedly exposes the an implementation detail, its "preferred alignment" for the type, rather than the formal/ABI alignment of the type, which it only actually uses in structures. on most archs the two values are the same, but on some (at least i386) the preferred alignment is greater than the ABI alignment. I considered using _Alignas(8) unconditionally, but on at least one arch (or1k), the alignment of max_align_t with GCC's definition is only 4 (even the "preferred alignment" for these types is only 4).
2013-11-24restore type of NULL to void * except when used in C++ programsRich Felker-0/+4
unfortunately this eliminates the ability of the compiler to diagnose some dangerous/incorrect usage, but POSIX requires (as an extension to the C language, i.e. CX shaded) that NULL have type void *. plain C allows it to be defined as any null pointer constant. the definition 0L is preserved for C++ rather than reverting to plain 0 to avoid dangerous behavior in non-conforming programs which use NULL as a variadic sentinel. (it's impossible to use (void *)0 for C++ since C++ lacks the proper implicit pointer conversions, and other popular alternatives like the GCC __null extension seem non-conforming to the standard's requirements.)
2013-01-18use a common definition of NULL as 0L for C and C++Rich Felker-6/+1
the historical mess of having different definitions for C and C++ comes from the historical C definition as (void *)0 and the fact that (void *)0 can't be used in C++ because it does not convert to other pointer types implicitly. however, using plain 0 in C++ exposed bugs in C++ programs that call variadic functions with NULL as an argument and (wrongly; this is UB) expect it to arrive as a null pointer. on 64-bit machines, the high bits end up containing junk. glibc dodges the issue by using a GCC extension __null to define NULL; this is observably non-conforming because a conforming application could observe the definition of NULL via stringizing and see that it is neither an integer constant expression with value zero nor such an expression cast to void. switching to 0L eliminates the issue and provides compatibility with broken applications, since on all musl targets, long and pointers have the same size, representation, and argument-passing convention. we could maintain separate C and C++ definitions of NULL (i.e. just use 0L on C++ and use (void *)0 on C) but after careful analysis, it seems extremely difficult for a C program to even determine whether NULL has integer or pointer type, much less depend in subtle, unintentional ways, on whether it does. C89 seems to have no way to make the distinction. on C99, the fact that (int)(void *)0 is not an integer constant expression, along with subtle VLA/sizeof semantics, can be used to make the distinction, but many compilers are non-conforming and give the wrong result to this test anyway. on C11, _Generic can trivially make the distinction, but it seems unlikely that code targetting C11 would be so backwards in caring which definition of NULL an implementation uses. as such, the simplest path of using the same definition for NULL in both C and C++ was chosen. the #undef directive was also removed so that the compiler can catch and give a warning or error on redefinition if buggy programs have defined their own versions of NULL prior to inclusion of standard headers.
2012-12-05use __builtin_offsetof to implement offsetof when possibleRich Felker-0/+4
apparently recent gcc versions have intentionally broken the traditional definition by treating it as a non-constant expression. the traditional definition may also be problematic for c++ programs.
2011-02-12initial check-in, version 0.5.0v0.5.0Rich Felker-0/+19