argv[0]

argv[0]

[a.biardi]

Hi,

Is there any C function that can tell me what argv[0] is, outside 
main()?

I thought to use getpid() and then look at /proc/<pid>/cmdline but 
doesn't seem portable. Any hints?

Thanks,
Andrea.

Re: argv[0]

[wwp]

[-- Attachment #1: Type: text/plain, Size: 590 bytes --]

Hello Andrea,


On Fri, 13 Jan 2006 00:16:23 +0100 a.biardi@tiscali.it wrote:

> 
> Hi,
> 
> Is there any C function that can tell me what argv[0] is, outside 
> main()?
> 
> I thought to use getpid() and then look at /proc/<pid>/cmdline but 
> doesn't seem portable. Any hints?

For instance, in main(), you can store argc and argv into global const
pointers that you can use anywhere else.

Here's an example (see the attached files):

$ gcc main.c elsewhere.c
$ ./a.out

shows:
main: 1 0xbf8526f4 './a.out'
sample1: 1 0xbf8526f4 './a.out'
sample2: 1 0xbf8526f4 './a.out'


HTH,

-- 
wwp

[-- Attachment #2: elsewhere.c --]
[-- Type: text/x-csrc, Size: 168 bytes --]

#include <stdio.h>

extern int prg_argc;
extern char** prg_argv;

void outside_from_main_2(void)
{
	printf("sample2: %d %p '%s'\n", prg_argc, prg_argv, prg_argv[0]);
}

[-- Attachment #3: elsewhere.h --]
[-- Type: text/x-chdr, Size: 32 bytes --]

void outside_from_main_2(void);

[-- Attachment #4: main.c --]
[-- Type: text/x-csrc, Size: 341 bytes --]

#include <stdio.h>

int prg_argc=0;
char** prg_argv=NULL;

void outside_from_main_1(void)
{
	printf("sample1: %d %p '%s'\n", prg_argc, prg_argv, prg_argv[0]);
}

int main(int argc, char** argv)
{
	printf("main: %d %p '%s'\n", argc, argv, argv[0]);
	prg_argc=argc;
	prg_argv=argv;
	outside_from_main_1();
	outside_from_main_2();

	exit(0);
}

Re: argv[0]

[a.biardi]

On Friday 13 January 2006 10:52, you wrote:

> Hello Andrea,
>
> On Fri, 13 Jan 2006 00:16:23 +0100 a.biardi@tiscali.it wrote:
> > Hi,
> >
> > Is there any C function that can tell me what argv[0] is, outside
> > main()?
> >
> > I thought to use getpid() and then look at /proc/<pid>/cmdline
> > but doesn't seem portable. Any hints?
>
> For instance, in main(), you can store argc and argv into global
> const pointers that you can use anywhere else.
>
> Here's an example (see the attached files):
>
> $ gcc main.c elsewhere.c
> $ ./a.out
>
> shows:
> main: 1 0xbf8526f4 './a.out'
> sample1: 1 0xbf8526f4 './a.out'
> sample2: 1 0xbf8526f4 './a.out'
>
>
> HTH,

Thanks, I know that. But I am developing a library, and have no access 
to the real main().

I could ask the user of my library to place a call to an init() 
function in main(), passing argv[0] along, but I don't like this 
solution very much.

Assuming I don't have access to main(), is there any other way to 
retrieve argv[0]?

Thanks,
Andrea.

Re: argv[0]

[Neil Horman]

On Fri, Jan 13, 2006 at 12:52:26PM +0100, a.biardi@tiscali.it wrote:
> On Friday 13 January 2006 10:52, you wrote:
> 
> > Hello Andrea,
> >
> > On Fri, 13 Jan 2006 00:16:23 +0100 a.biardi@tiscali.it wrote:
> > > Hi,
> > >
> > > Is there any C function that can tell me what argv[0] is, outside
> > > main()?
> > >
> > > I thought to use getpid() and then look at /proc/<pid>/cmdline
> > > but doesn't seem portable. Any hints?
> >
> > For instance, in main(), you can store argc and argv into global
> > const pointers that you can use anywhere else.
> >
> > Here's an example (see the attached files):
> >
> > $ gcc main.c elsewhere.c
> > $ ./a.out
> >
> > shows:
> > main: 1 0xbf8526f4 './a.out'
> > sample1: 1 0xbf8526f4 './a.out'
> > sample2: 1 0xbf8526f4 './a.out'
> >
> >
> > HTH,
> 
> Thanks, I know that. But I am developing a library, and have no access 
> to the real main().
> 
> I could ask the user of my library to place a call to an init() 
> function in main(), passing argv[0] along, but I don't like this 
> solution very much.
> 
> Assuming I don't have access to main(), is there any other way to 
> retrieve argv[0]?
> 
This probably isn't too much more portable than interrogating
/proc/<pid>/cmdline, but I expect that since argv is passed in on the stack to
main, you could probably compute the top of the applications stack, and find the
argv pointer that way.  You may have to make a few assumptions about the system
architecture, but it can be done.  Check out the backtrace function in glibc for
an example (at least on x86) of how finding the top of stack is done there.

Regards
Neil

> Thanks,
> Andrea.
> -
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-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *gpg keyid: 1024D / 0x92A74FA1 - http://pgp.mit.edu
 ***************************************************/

Re: argv[0]

[Steve Graegert]

On 1/13/06, a.biardi@tiscali.it <a.biardi@tiscali.it> wrote:
>
> Hi,
>
> Is there any C function that can tell me what argv[0] is, outside
> main()?
>
> I thought to use getpid() and then look at /proc/<pid>/cmdline but
> doesn't seem portable. Any hints?

The arguments are pushed on the stack upon process creation.  Once the
process is running there is little chance to get hands on them except
for the /proc approach.

	\Steve

--

Steve Graegert <graegerts@gmail.com>
Software Consultant {C/C++ && Java && .NET}
Office: +49 9131 7123988
Mobile: +49 1520 9289212

Re: argv[0]

[a.biardi]

On Friday 13 January 2006 13:26, you wrote:

> On 1/13/06, a.biardi@tiscali.it <a.biardi@tiscali.it> wrote:
> > Hi,
> >
> > Is there any C function that can tell me what argv[0] is, outside
> > main()?
> >
> > I thought to use getpid() and then look at /proc/<pid>/cmdline
> > but doesn't seem portable. Any hints?
>
> The arguments are pushed on the stack upon process creation.  Once
> the process is running there is little chance to get hands on them
> except for the /proc approach.
>
> 	\Steve
>

Just in case anybody needs it, I think I found something inside 
errno.h (GNU-only):

/* The full and simple forms of the name with which the program was
   invoked.  These variables are set up automatically at startup based
   on  the value of ARGV[0] (this works only if you use GNU ld). */
extern char *program_invocation_name, *program_invocation_short_name;¶

Bye,
Andrea.
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