environmental variables

[Casanova]

Hello!!

how can i get all the details of the environmental variables. If i use
getenv, i will have to specify the name of the variable. for intsance i
will have to give getenv("PATH")

How can i get the information of all the variables, with the variable
names and its values

Pls Help

Casanova

[Satya Das]

/*
This program should print all the environment variables.
*/
#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )
{
for( int i = 0; envp[i] != NULL; ++i )
{
printf("%s\n", envp[i]);
}

return 0;
}
"Casanova" <pr********@gma il.com> wrote in message
news:11******** **************@ z14g2000cwz.goo glegroups.com.. .

Hello!!

how can i get all the details of the environmental variables. If i use
getenv, i will have to specify the name of the variable. for intsance i
will have to give getenv("PATH")

How can i get the information of all the variables, with the variable
names and its values

Pls Help

Casanova

[Joona I Palaste]

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/
Only on some implementations .
#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )
This form of main() is non-standard and causes undefined behaviour.
It might work for some implementations but is not guaranteed to work
on any.
{
for( int i = 0; envp[i] != NULL; ++i )
{
printf("%s\n", envp[i]);
} return 0;
}

--
/-- Joona Palaste (pa*****@cc.hel sinki.fi) ------------- Finland --------\
\-------------------------------------------------------- rules! --------/
"I will never display my bum in public again."
- Homer Simpson

[Bjørn Augestad]

Joona I Palaste wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/

Only on some implementations .

#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )

This form of main() is non-standard and causes undefined behaviour.

Hmm, the C99 standard says in 5.1.2.2.1 Program startup, that main() is
defined
a) "... with no parameters"
b) "... or with two parameters"
c) "..., or in some other implementation-defined manner".

That's not undefined and should not cause nasal daemons or anything
else, should it? ;-)

Bjørn
[snip]

[Jens.Toerring]

Joona I Palaste <pa*****@cc.hel sinki.fi> wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/

Only on some implementations . #include <stdio.h>
int main( int argc, char *argv[], char *envp[] )

This form of main() is non-standard and causes undefined behaviour.
It might work for some implementations but is not guaranteed to work
on any.

Just taking a closer look I found in the standard (C89):

In a hosted environment, the main function receives a third
argument, char *envp[], that points to a null-terminated array of
pointers to char, each of which points to a string that provides
information about the environment for this execution of the process

but which seems to contradict what's written further up about the
arguments of main() for a hosted environment:

The function called at program startup is named main. The
implementation declares no prototype for this function. It can be
defined with no parameters:

int main(void) { /*...*/ }

or with two parameters (referred to here as argc and argv, though any
names may be used, as they are local to the function in which they are
declared):

int main(int argc, char *argv[]) { /*...*/ }

Can someone shed some light on this? Is that why in C99 the extra
clause "or in some other implementation-defined manner" got added
(but they kept the requirement for the third, *envp argument, not
declaring that as also "implementa tion-defined")? Or does main()
receive a third argument but you're not allowed to put it into its
definition (but which would seem to be silly)?

Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de

[Eric Sosman]

Je***********@p hysik.fu-berlin.de wrote:

Joona I Palaste <pa*****@cc.hel sinki.fi> wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/

Only on some implementations .

#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )

This form of main() is non-standard and causes undefined behaviour.
It might work for some implementations but is not guaranteed to work
on any.

Just taking a closer look I found in the standard (C89):

In a hosted environment, the main function receives a third
argument, char *envp[], that points to a null-terminated array of
pointers to char, each of which points to a string that provides
information about the environment for this execution of the process
[...]

The quoted text is from an appendix titled "Common
extensions." The paragraph immediately before the quote
begins

The following extensions are widely used in many
systems, but are not portable to all implementations .

Other nearby paragraphs mention such things as dollar
signs in identifiers, modifiable string literals, casting
data pointers to function pointers, the `asm' keyword, and
so on. Like the `envp' argument, all are non-Standard.

--
Er*********@sun .com

[Lawrence Kirby]

On Fri, 10 Dec 2004 12:33:52 +0000, Jens.Toerring wrote:

Joona I Palaste <pa*****@cc.hel sinki.fi> wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/

Only on some implementations .

And it is mostly deprecated even on those now. For reference the POSIX way
is to use an extern char **environ variable.

#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )

This form of main() is non-standard and causes undefined behaviour.
It might work for some implementations but is not guaranteed to work
on any.

Just taking a closer look I found in the standard (C89):

In a hosted environment, the main function receives a third
argument, char *envp[], that points to a null-terminated array of
pointers to char, each of which points to a string that provides
information about the environment for this execution of the process

I believe you found this in an non-normative annex under a section called
"Common Extensions". I.e. this text is NOT part of the standard definition
of the C language.
but which seems to contradict what's written further up about the
arguments of main() for a hosted environment:

The function called at program startup is named main. The
implementation declares no prototype for this function. It can be
defined with no parameters:

int main(void) { /*...*/ }

or with two parameters (referred to here as argc and argv, though any
names may be used, as they are local to the function in which they are
declared):

int main(int argc, char *argv[]) { /*...*/ }

Can someone shed some light on this? Is that why in C99 the extra
clause "or in some other implementation-defined manner" got added
(but they kept the requirement for the third, *envp argument, not
declaring that as also "implementa tion-defined")? Or does main()
receive a third argument but you're not allowed to put it into its
definition (but which would seem to be silly)?

There is NO three argument form of main() in standard C. It is simply
recognised in the standard document as a common extension. C99 allows
implementation-defined extensions. All this means is that if an
implementation supports any forms of main() other than the 2 above (and
those compatible with them) it must document them. There is no requirement
that a particular implementation supports specific other forms such as the
envp one, and code that uses them results in undefined behvaiour as far as
the standard is concerned.

Lawrence

[Jens.Toerring]

Eric Sosman <er*********@su n.com> wrote:

Je***********@p hysik.fu-berlin.de wrote:

Just taking a closer look I found in the standard (C89):

In a hosted environment, the main function receives a third
argument, char *envp[], that points to a null-terminated array of
pointers to char, each of which points to a string that provides
information about the environment for this execution of the process
[...]

The quoted text is from an appendix titled "Common
extensions." The paragraph immediately before the quote
begins The following extensions are widely used in many
systems, but are not portable to all implementations .

I see, thanks. Should have scrolled up instead of just down, not
really caring for anything that didn't contain the string "env"...

Regards, Jens
--
\ Jens Thoms Toerring ___ Je***********@p hysik.fu-berlin.de
\______________ ____________ http://www.toerring.de

[Flash Gordon]

On Fri, 10 Dec 2004 12:18:35 GMT
Bjørn Augestad <bo*@metasystem s.no> wrote:

Joona I Palaste wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:

/*
This program should print all the environment variables.
*/

Only on some implementations .

#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )

This form of main() is non-standard and causes undefined behaviour.

Hmm, the C99 standard says in 5.1.2.2.1 Program startup, that main()
is defined
a) "... with no parameters"
b) "... or with two parameters"
c) "..., or in some other implementation-defined manner".

That's not undefined and should not cause nasal daemons or anything
else, should it? ;-)

Surely that means that if the implementation defines another prototype
it is implementation defined but if you do something neither explicitly
defined by the C standard nor the implementation then it is undefined
behaviour. So on a Posix system it may be defined (by the
implementation) but on Windows it might invoke undefined behaviour.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Bjørn Augestad]

Flash Gordon wrote:

On Fri, 10 Dec 2004 12:18:35 GMT
Bjørn Augestad <bo*@metasystem s.no> wrote:

Joona I Palaste wrote:

Satya Das <sa************ **@yahoo.com> scribbled the following:
/*
This program should print all the environment variables.
*/
Only on some implementations .

#include <stdio.h>
int main( int argc, char *argv[], char *envp[] )
This form of main() is non-standard and causes undefined behaviour.

Hmm, the C99 standard says in 5.1.2.2.1 Program startup, that main()
is defined
a) "... with no parameters"
b) "... or with two parameters"
c) "..., or in some other implementation-defined manner".

That's not undefined and should not cause nasal daemons or anything
else, should it? ;-)

Surely that means that if the implementation defines another prototype
it is implementation defined but if you do something neither explicitly
defined by the C standard nor the implementation then it is undefined
behaviour. So on a Posix system it may be defined (by the
implementation) but on Windows it might invoke undefined behaviour.

If a prototype for main() is neither according to the standard nor
supported by the implementation, I would expect a diagnostic message to
be printed instead of just silently allowing it and possibly invoke
undefined behaviour.

Now that I have tried it, I am not so sure anymore. gcc -std=c99 is
silent on the foo parameter unless -Wall is used, even if it reports
that main() doesn't return int. MSVC happily accepts the code, even when
/Za /W4 is used. :-|

Bjørn

$ cat m2.c
#include <stdio.h>

float main(int ac, char*av[], char**envp, char**foo)
{
while(*envp)
printf("%s\n", *envp++);

return 0;
}

boa@wintendo /tmp
$ gcc -std=c99 m2.c
m2.c: In function `main':
m2.c:4: warning: return type of `main' is not `int'

boa@wintendo /tmp
$ gcc -std=c99 -Wall m2.c
m2.c:4: warning: return type of `main' is not `int'
m2.c:4: warning: `main' takes only zero or two arguments

boa@wintendo /tmp
$