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Date: Mon, 7 Mar 2022 08:18:47 -0500
From: Rich Felker <dalias@...c.org>
To: "wangjianjian (C)" <wangjianjian3@...wei.com>
Cc: musl@...ts.openwall.com
Subject: Re: basename with no parameter?
On Mon, Mar 07, 2022 at 10:31:41AM +0800, wangjianjian (C) wrote:
> Hi all,
>
> I find that the basename in string.h with _GNU_SOURCE in Musl
> libc(Line 119):
>
> char *basename();
This is not a declaration with no parameter. It's a declaration
without any prototype.
> The man page says that have two different version of basename
> however both need one parameter, is this correct?
No, that's documenting glibc. There is only one version of basename in
musl and it's the standard one.
The reason for the non-prototype declaration is explained in commit
37bb3cce4598c19288628e675eaf1cda6e96958f:
omit declaration of basename wrongly interpreted as prototype in C++
the non-prototype declaration of basename in string.h is an ugly
compromise to avoid breaking 2 types of broken software:
1. programs which assume basename is declared in string.h and thus
would suffer from dangerous pointer-truncation if an implicit
declaration were used.
2. programs which include string.h with _GNU_SOURCE defined but then
declare their own prototype for basename using the incorrect GNU
signature for the function (which would clash with a correct
prototype).
however, since C++ does not have non-prototype declarations and
interprets them as prototypes for a function with no arguments, we
must omit it when compiling C++ code. thankfully, all known broken
apps that suffer from the above issues are written in C, not C++.
This was from 2012, so it might make sense to do something different
now, like putting the correct prototype there and getting any programs
it still clashes with fixed.
Rich
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