determining function name in runtime

**Vladimir S. Oka** · Mar 2 '06, 02:35 PM

Re: determining function name in runtime

shyam wrote:[color=blue]
> Hi all
>
> is there any way the determine which function currently is executing in
> a process ?[/color]

I assume you mean program...
[color=blue]
>
> For example we can find the file name using __FILE__
> and line number using __LINE__ macros
>
> simillarly is there any macro which gives the function name[/color]

Yes, and it's __func__ (note double underscores before and after).

--
BR, Vladimir

**Lew Pitcher** · Mar 2 '06, 02:55 PM

Re: determining function name in runtime

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Vladimir S. Oka wrote:[color=blue]
> shyam wrote:[color=green]
>> Hi all
>>
>> is there any way the determine which function currently is executing in
>> a process ?[/color]
>
> I assume you mean program...
>[color=green]
>> For example we can find the file name using __FILE__
>> and line number using __LINE__ macros
>>
>> simillarly is there any macro which gives the function name[/color]
>
> Yes, and it's __func__ (note double underscores before and after).[/color]

Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
predefined identifier of local (to the function) scope.

Thus,
char *where_I_am = "I am at line " __LINE__ "\n";
would work, but
char *where_I_am = "I am in function " __func__ "\n";
would not.

OTOH,
printf("I am at line %d in function %s\n",__LINE__, __func__);
will work.

- --

Lew Pitcher, IT Specialist, Corporate Technology Solutions,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.2 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFEBwFDagV FX4UWr64RAlQdAJ 9XT4qQS65GzFFRP O0RDFqxskDA+wCd GWGd
evG1lEWtpMvGxVd vP/Y97RM=
=vy6r
-----END PGP SIGNATURE-----

**MrG{DRGN}** · Mar 2 '06, 04:25 PM

Re: determining function name in runtime

"Lew Pitcher" <Lew.Pitcher@td securities.com> wrote in message
news:8jDNf.4274 $RM2.570635@new s20.bellglobal. com...[color=blue]
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Vladimir S. Oka wrote:[/color]
-snip

, and it's __func__ (note double underscores before and after).[color=blue]
>
> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
> predefined identifier of local (to the function) scope.
>
> Thus,
> char *where_I_am = "I am at line " __LINE__ "\n";
> would work, but
> char *where_I_am = "I am in function " __func__ "\n";
> would not.
>
> OTOH,
> printf("I am at line %d in function %s\n",__LINE__, __func__);
> will work.
>
>[/color]

Let me guess, __func__ is a C99 feature?
<OT> (which means I can't use it with my compiler msvc 6.0).<OT>

--
MrG{DRGN}

**Vladimir S. Oka** · Mar 2 '06, 04:35 PM

Re: determining function name in runtime

MrG{DRGN} wrote:[color=blue]
> "Lew Pitcher" <Lew.Pitcher@td securities.com> wrote in message
> news:8jDNf.4274 $RM2.570635@new s20.bellglobal. com...[color=green]
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Vladimir S. Oka wrote:[/color]
> -snip
>
> , and it's __func__ (note double underscores before and after).[color=green]
> >
> > Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
> > predefined identifier of local (to the function) scope.
> >
> > Thus,
> > char *where_I_am = "I am at line " __LINE__ "\n";
> > would work, but
> > char *where_I_am = "I am in function " __func__ "\n";
> > would not.
> >
> > OTOH,
> > printf("I am at line %d in function %s\n",__LINE__, __func__);
> > will work.
> >
> >[/color]
>
> Let me guess, __func__ is a C99 feature?
> <OT> (which means I can't use it with my compiler msvc 6.0).<OT>[/color]

Yes it is.
<OT>I know nothing about M$VC, but it may provide it as an
extension?<OT>

**Ico** · Mar 2 '06, 04:45 PM

Re: determining function name in runtime

Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
[color=blue]
> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
> predefined identifier of local (to the function) scope.[/color]

Is there a reason why __func__ is not a macro ?

--
:wq
^X^Cy^K^X^C^C^C ^C

**tmp123** · Mar 2 '06, 04:55 PM

Re: determining function name in runtime

Ico wrote:[color=blue]
> Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
>[color=green]
> > Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
> > predefined identifier of local (to the function) scope.[/color]
>
>
> Is there a reason why __func__ is not a macro ?
>[/color]

It is easy for the preprocessor to know the current file and line.
However, it can not known the function name (even it can not known what
is a function) if it doesn't knowns C syntax (and the preprocessor
doesn't).

**Lew Pitcher** · Mar 2 '06, 05:15 PM

Re: determining function name in runtime

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Ico wrote:[color=blue]
> Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
>[color=green]
>> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
>> predefined identifier of local (to the function) scope.[/color]
>
>
> Is there a reason why __func__ is not a macro ?[/color]

My copy of the draft C99 standard doesn't give a reason.

My /guess/ is that __FILE__ and __LINE__ can be implemented as macros
because they do not require any interpretation of the C code (they are
strictly derived from the mechanics of reading the source files).

OTOH, __func__ requires the compiler's interpretation of the code in
order to work, so it cannot be implemented in the same manner as __FILE_
and __LINE__.

- --

Lew Pitcher, IT Specialist, Corporate Technology Solutions,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.2 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFEByGZagV FX4UWr64RAjQJAJ 9unyR7P+JPi14Yw Ci+eKaYF+VeMgCg s0N/
yRzUKfTTmLVMySm RWJUv6us=
=KubY
-----END PGP SIGNATURE-----

**Micah Cowan** · Mar 2 '06, 07:35 PM

Re: determining function name in runtime

"tmp123" <tmp123@menta.n et> writes:
[color=blue]
> Ico wrote:[color=green]
> > Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
> >[color=darkred]
> > > Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
> > > predefined identifier of local (to the function) scope.[/color]
> >
> >
> > Is there a reason why __func__ is not a macro ?
> >[/color]
>
> It is easy for the preprocessor to know the current file and line.
> However, it can not known the function name (even it can not known what
> is a function) if it doesn't knowns C syntax (and the preprocessor
> doesn't).[/color]

s/doesn't/might not/

Several implementations have provided such a macro. While they /may/
have been handled differently from other macros (I don't actually
know), they were still handled as string literals, and thus you could
make use of the concatenation feature, etc.

But I think the reason you give above is at least why the standard
didn't want to /require/ __func__ to be a macro (and so they required
it to be something else).

-Micah

**Jordan Abel** · Mar 2 '06, 10:05 PM

Re: determining function name in runtime

On 2006-03-02, MrG{DRGN} <Iamnot@here.co m> wrote:[color=blue]
>
> "Lew Pitcher" <Lew.Pitcher@td securities.com> wrote in message
> news:8jDNf.4274 $RM2.570635@new s20.bellglobal. com...[color=green]
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Vladimir S. Oka wrote:[/color]
> -snip
>
> , and it's __func__ (note double underscores before and after).[color=green]
>>
>> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
>> predefined identifier of local (to the function) scope.
>>
>> Thus,
>> char *where_I_am = "I am at line " __LINE__ "\n";
>> would work, but
>> char *where_I_am = "I am in function " __func__ "\n";
>> would not.
>>
>> OTOH,
>> printf("I am at line %d in function %s\n",__LINE__, __func__);
>> will work.
>>
>>[/color]
>
> Let me guess, __func__ is a C99 feature?
> <OT> (which means I can't use it with my compiler msvc 6.0).<OT>[/color]

No, but i have a suggestion:

#if __STDC_VERSION_ _ < 199901l
#define WHERE_FMT __FILE__ ":%d"
#define WHERE_ARGS __LINE__
#else
#define WHERE_FMT __FILE__ ":%s:%d"
#define WHERE_ARGS __LINE__,__func __
#endif

fprintf(stderr, "Line printed to stderr at "WHERE_FMT"\n", WHERE_ARGS);

will print file.c:function :42 on c99 systems, file.c:42 on others.

**Jordan Abel** · Mar 2 '06, 10:05 PM

Re: determining function name in runtime

On 2006-03-02, Lew Pitcher <Lew.Pitcher@td securities.com> wrote:[color=blue]
>
> Ico wrote:[color=green]
>> Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
>>[color=darkred]
>>> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
>>> predefined identifier of local (to the function) scope.[/color]
>>
>>
>> Is there a reason why __func__ is not a macro ?[/color]
>
> My copy of the draft C99 standard doesn't give a reason.[/color]

That's because that's not the right place to look

http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf

lines 29-31 on page 50 [PDF page 57] read as follows:

A new feature of C99: C99 introduces predefined identifiers, which have
block scope (as distinct 30 from predefined macros which have file
scope), and one such predefined identifier, __func__, which allows the
function name to be used at execution time.

That seems to be saying that the reason is because a macro has file
scope, and thus couldn't have a different value on different lines
unless undefined and redefined by the user.

Note, however, that string literal concatenation takes place in phase 6,
whereas semantic analysis [which is when { } becomes a block scope, etc]
is phase 7.

**Ben Bacarisse** · Mar 3 '06, 12:15 AM

Re: determining function name in runtime

On Thu, 02 Mar 2006 21:48:10 +0000, Jordan Abel wrote:
[color=blue]
> No, but i have a suggestion:
>
> #if __STDC_VERSION_ _ < 199901l
> #define WHERE_FMT __FILE__ ":%d"
> #define WHERE_ARGS __LINE__
> #else
> #define WHERE_FMT __FILE__ ":%s:%d"[/color]

Micro correction: swap %s and %d (or __LINE__ and __func__ below)
[color=blue]
> #define WHERE_ARGS __LINE__,__func __
> #endif
>
> fprintf(stderr, "Line printed to stderr at "WHERE_FMT"\n", WHERE_ARGS);[/color]

--
Ben.

**Keith Thompson** · Mar 3 '06, 01:05 AM

Re: determining function name in runtime

Jordan Abel <random832@gmai l.com> writes:[color=blue]
> On 2006-03-02, Lew Pitcher <Lew.Pitcher@td securities.com> wrote:[color=green]
>>
>> Ico wrote:[color=darkred]
>>> Lew Pitcher <Lew.Pitcher@td securities.com> wrote:
>>>
>>>> Note: Unlike __FILE__ and __LINE__, __func__ is not a macro, but a
>>>> predefined identifier of local (to the function) scope.
>>>
>>>
>>> Is there a reason why __func__ is not a macro ?[/color]
>>
>> My copy of the draft C99 standard doesn't give a reason.[/color]
>
> That's because that's not the right place to look
> http://www.open-std.org/jtc1/sc22/wg...onaleV5.10.pdf
>
> lines 29-31 on page 50 [PDF page 57] read as follows:
>
> A new feature of C99: C99 introduces predefined identifiers, which have
> block scope (as distinct 30 from predefined macros which have file
> scope), and one such predefined identifier, __func__, which allows the
> function name to be used at execution time.
>
> That seems to be saying that the reason is because a macro has file
> scope, and thus couldn't have a different value on different lines
> unless undefined and redefined by the user.[/color]

__LINE__ has a different value on different lines, and the
preprocessor has no problem handling that.

__func__ isn't a macro because making it one would have required the
preprocessor (more precisely, translation phase 4) to understand more
of the language grammar than is currently required.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.