How to look up where a structure is defined?

[Peng Yu]

On 3/3/21, Konstantin Kharlamov <hi-angel@yandex.ru> wrote:
> On Wed, 2021-03-03 at 16:24 -0600, Peng Yu wrote:
>> On Wed, Mar 3, 2021 at 2:23 PM Konstantin Kharlamov <hi-angel@yandex.ru>
>> wrote:
>> >
>> > On Wed, 2021-03-03 at 23:09 +0300, Konstantin Kharlamov wrote:
>> > > On Wed, 2021-03-03 at 13:51 -0600, Peng Yu wrote:
>> > > > This seems to be a complicated solution. I just want to get a
>> > > > database
>> > > > (a TSV file should be fine) of types and the header they appear. I
>> > > > don't want to build the project just to get this info.
>> > >
>> > > I see, well, the Universal Ctags I mentioned should work for you. It
>> > > doesn't
>> > > require building the project: you just run `ctags -R` or `ctags -Re`
>> > > (first
>> > > for
>> > > vim-style tags file, second one for emacs-style) over the repository,
>> > > and
>> > > you
>> > > get a `tags` or `TAGS` file with a list of definitions.
>> > >
>> > > Possible drawbacks on ctags I mentioned in the other email. Basically
>> > > it's
>> > > that
>> > > it doesn't take context into consideration.
>> > >
>> > > Regarding usage: the tags file it generates, although can be read for
>> > > human,
>> > > supposed to be read by text editors/IDEs. Since you mention a CSV
>> > > file, I
>> > > assume
>> > > you might want something human-readable. Please see option --output-
>> > > format= in
>> > > `man ctags` for details: I think you might want the `xref` format. (I
>> > > never
>> > > tried it myself, just reading the man it seems like it what you're
>> > > after).
>> >
>> > Although, I wouldn't hold my breath that reading a resulting xref file
>> > would
>> > be easy The reason being is that I expect a tags file created from
>> > glibc
>> > repo to be some hundreds of megabytes. For reference, a TAGS file I
>> > generated long ago for libreoffice project is sized at 183M.
>> >
>> > So yeah, you will probably want to use the file from an IDE or text
>> > editor,
>> > rather than reading it manually.
>>
>> ctags can partially solve the problem. The declaration and definition
>> of a struct are all in the header. So finding the definition is OK.
>> But it can not return function declaration. Is there a way to show
>> function declaration as well? (For example, ./socket/sys/socket.h for
>> setsockopt().)
>>
>> $ grep '^icmphdr\>' tags
>> icmphdr sysdeps/gnu/netinet/ip_icmp.h /^struct icmphdr$/;" s
>> $ grep ^setsockopt tags
>> setsockopt sysdeps/unix/sysv/linux/setsockopt.c /^setsockopt (int fd,
>> int level, int optname, const void *optval, socklen_t len)$/;" f

ctags only shows the above. The following is what I show where the
declaration is.

>> ./socket/sys/socket.h
>> 215:extern int setsockopt (int __fd, int __level, int __optname,
>
> But, in the grep output you show you have both the declaration and the
> definition of setsockopt, no? In particular, you have the declaration from
> `socket.h` file.
>
> I think you're confused because your editor/IDE navigates by default to the
> first match in the tags file, which probably happened to be the definition.
> I know vim does that in particular. What to do here is depends on the
> editor/IDE you're using. For vim specifically there is some command to go to
> the next tag (I think it's `:tn`).
>
> In Emacs it is implemented in a better way: it shows you a list of all
> matches when there's more than one, and you get to chose which one you want.
> Idk, perhaps there's a plugin that implements similar behavior for vim…?
> Anyway, point being is that the answer depends on what you're using with the
> tags file.
>
> On a side note, you do need to figure it out for your editor/IDE, because,
> for example, with struct fields you might get tons of matches, depending on
> circumstances. Remember, tags does not include context. So if project has
> multiple structs with a field `int foo;`, all of them will match when you'll
> try navigate to `foo` by using tags.
>
>


-- 
Regards,
Peng