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DevSolar / pdclib

The Public Domain C Library
https://pdclib.rootdirectory.de
Creative Commons Zero v1.0 Universal
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NULL is not detected as a sentinel #13

Closed thrimbor closed 4 years ago

thrimbor commented 4 years ago

We came across this a while ago in https://github.com/XboxDev/nxdk/issues/253. Code can use a special attribute on gcc and clang that signals the compiler that it should check whether calls to the function use a sentinel value to properly end the parameter list. This warning gets emitted when using PDCLib even when properly using NULL as a sentinel value, because NULL is defined as a zero literal: https://github.com/DevSolar/pdclib/blob/108299a1157e6872d60936d6e1481d2dbaad2737/include/pdclib/_PDCLIB_int.h#L19

clang has a test for this warning which indicates that it expects a pointer type: https://github.com/llvm-mirror/clang/blob/master/test/Sema/block-sentinel-attribute.c

The C11 standard says in 7.19:

NULL which expands to an implementation-defined null pointer constant;

So I think replacing the above line with something #define _PDCLIB_NULL ((void *)0) should resolve that without any drawbacks regarding portability or standard compliance.

DevSolar commented 4 years ago

This was one of the first definitions I made... and I had hoped to get away without #ifdef __cplusplus (because C++ defines NULL as literal 0, and C doesn't care much whether it is a pointer type or not in virtually all places)...

But by now we have lots of __cplusplus checks anyway, so why not here. This will be quickly done, but might take a couple of days extra before I push to git, as I want to have the changes necessitated by freopen() all cleaned up and properly commented first.

thrimbor commented 4 years ago

Afaik C++11 and higher even allow NULL to be defined as nullptr, while clang seems to use __null when building C++ code (seems to be a GCC/LLVM thing only). Not sure whether it may be a good idea to go for one of these, though.

DevSolar commented 4 years ago

Added a three-way selection for C ((void*)0), C++98 (0), and C++11 and later (nullptr).

Only in SVN until I get the rest cleaned up as well.

https://rootdirectory.ddns.net/websvn/filedetails.php?repname=PDCLib&path=%2Ftrunk%2Finclude%2Fpdclib%2F_PDCLIB_int.h

Does this float your boat?

thrimbor commented 4 years ago

That should be fine, thanks!