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  • Invalid sample definition for errno

    From Keith Thompson@Keith.S.Thompson+u@gmail.com to comp.std.c on Sat Nov 19 18:08:13 2022
    From Newsgroup: comp.std.c

    A footnote in the section describing <errno.h> says:

    The macro errno need not be the identifier of an object. It might
    expand to a modifiable lvalue resulting from a function call (for
    example, *errno()).

    Footnotes are non-normative, and this one is presumably intended to be informal, but that's not a valid macro definition for errno, both
    because it's not fully protected by parentheses and because the function
    can't be named "errno".

    A valid definition (and the one used by glibc) is:

    # define errno (*__errno_location ())

    I suggest the footnote should be updated to use something like that
    (though it needn't show the entire #define directive).

    The same wording appears starting in C90 and up to and including the
    latest C23 draft.
    --
    Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
    Working, but not speaking, for XCOM Labs
    void Void(void) { Void(); } /* The recursive call of the void */
    --- Synchronet 3.19c-Linux NewsLink 1.113
  • From Tim Rentsch@tr.17687@z991.linuxsc.com to comp.std.c on Sun Nov 20 05:26:40 2022
    From Newsgroup: comp.std.c

    Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

    A footnote in the section describing <errno.h> says:

    The macro errno need not be the identifier of an object. It might
    expand to a modifiable lvalue resulting from a function call (for
    example, *errno()).

    Footnotes are non-normative, and this one is presumably intended to be informal, but that's not a valid macro definition for errno, both
    because it's not fully protected by parentheses and because the function can't be named "errno".

    I see no reason the function couldn't be named "errno".
    --- Synchronet 3.19c-Linux NewsLink 1.113
  • From Keith Thompson@Keith.S.Thompson+u@gmail.com to comp.std.c on Sun Nov 20 13:58:27 2022
    From Newsgroup: comp.std.c

    Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
    Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:
    A footnote in the section describing <errno.h> says:

    The macro errno need not be the identifier of an object. It might
    expand to a modifiable lvalue resulting from a function call (for
    example, *errno()).

    Footnotes are non-normative, and this one is presumably intended to be
    informal, but that's not a valid macro definition for errno, both
    because it's not fully protected by parentheses and because the function
    can't be named "errno".

    I see no reason the function couldn't be named "errno".

    My thought was that giving the function and the macro the same name
    would cause a conflict, and I thought I had an example that demonstrated
    it. Looking again, I was mistaken:

    If the name of the macro being replaced is found during this scan of
    the replacement list (not including the rest of the source file’s
    preprocessing tokens), it is not replaced.

    I still suggest that using the same name for both is needlessly
    confusing.
    --
    Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
    Working, but not speaking, for XCOM Labs
    void Void(void) { Void(); } /* The recursive call of the void */
    --- Synchronet 3.19c-Linux NewsLink 1.113