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[diff.mods.to.headers] Cover type-generic macro suppression #8665

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[diff.mods.to.headers] Cover type-generic macro suppression #8665

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4 changes: 3 additions & 1 deletion source/compatibility.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -3720,7 +3720,9 @@
The C headers \libheader{complex.h} and
\libheader{tgmath.h} do not contain any of the content from
the C standard library and instead merely include other headers from the \Cpp{}
standard library.
standard library. Whereas the \libheader{tgmath.h} macros can be suppressed in
C by, for example, using parentheses around the macro name, the \Cpp{} overload
sets cannot be bypassed in this manner; casts may be used instead.
Comment on lines +3723 to +3725
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@eisenwave eisenwave Dec 17, 2025

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This seems tutorial-like to be honest. The wording is clear that the tgmath.h macros don't exist in C++, and that's all that really needs to be said about compatibility differences.

Even if we want to have this new sentence, it seems like something that goes into a \begin{note} context.

I'm also not sure what you mean by "casts may be used instead". Are you casting the function itself to double(&)(double)? That isn't valid because of addressability restrictions. You could cast all the function arguments like sqrt((double)x), but that's possible in both languages, so it doesn't seem like it needs to be called out in [diff].

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@jensmaurer jensmaurer Dec 17, 2025

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I agree with the statement about casts; @hubert-reinterpretcast , please tell us what you mean by those "casts".

I do want to point out that Annex C is tutorial-like in nature (nothing new in that Annex, hopefully), so I'm not objecting to adding a clarifying sentence. However, I wonder whether an actual code example would convey the consequences more clearly.

#include <tgmath.h>

double x = (sqrt)(2.0f);   // calls sqrt(double) in C, but sqrt(float) in C++

Maybe just striking "casts may be used instead" is a way forward?

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@hubert-reinterpretcast hubert-reinterpretcast Dec 17, 2025

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please tell us what you mean by those "casts".

Yes, I meant casting the arguments to match the C non-macro function signature.


\rSec2[diff.mods.to.definitions]{Modifications to definitions}

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