program should print it's own variables

[sinbad]

how can i write a program, which should accept input as NAME of a
variable in the program and
print it's value.Is this possible. for example.

int main ()
{
int x,y,z;
x = 10;
y = 20;
z = 30;
wait_for_input( );
print_output();
}

wait_for_input ()
{
do some thing to get input from user;
}

print_output()
{
do some thing to print output;
}


the user gives the following commands at runtime.

#print x --it should print value of x
#print y --it should print vlaue of y


The solution should work even for structure variables.

thanks

[Jack Klein]

Re: program should print it's own variables

On Thu, 2 Oct 2008 19:21:25 -0700 (PDT), sinbad
<sinbad.sinbad@ gmail.comwrote in comp.lang.c:

how can i write a program, which should accept input as NAME of a
variable in the program and
print it's value.Is this possible. for example.
>
int main ()
{
int x,y,z;
x = 10;
y = 20;
z = 30;
wait_for_input( );
print_output();
}
>
wait_for_input ()
{
do some thing to get input from user;
}
>
print_output()
{
do some thing to print output;
}
>
>
the user gives the following commands at runtime.
>
#print x --it should print value of x
#print y --it should print vlaue of y

The FAQ for this group does not cover this exact situation, but it
does cover a similar one with a very similar solution:

Q: If I have a char * variable pointing to the name of a function, how
can I call that function?

You can read the answer to this question here:

http://c-faq.com/misc/symtab.html

It should be quite easy to figure out how to modify this to print the
values of various objects of the same type.

The solution should work even for structure variables.

You can use this technique to do that as well, it just takes more work
on your part.

thanks

--
Jack Klein
Home: http://JK-Technology.Com
FAQs for
comp.lang.c http://c-faq.com/
comp.lang.c++ http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++

http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

[sinbad]

Re: program should print it's own variables

On Oct 3, 8:27 am, Jack Klein <jackkl...@spam cop.netwrote:

On Thu, 2 Oct 2008 19:21:25 -0700 (PDT), sinbad
<sinbad.sin...@ gmail.comwrote in comp.lang.c:
>
>
>

how can i write a program, which should accept input as NAME of a
variable in the program and
print it's value.Is this possible. for example.

>

int main ()
{
 int x,y,z;
 x = 10;
 y = 20;
 z = 30;
 wait_for_input( );
 print_output();
}

>

wait_for_input ()
{
 do some thing to get input from user;
}

>

print_output()
{
 do some thing to print output;
}

>

the user gives the following commands at runtime.

>

#print x  --it should print value of x
#print y  --it should print vlaue of y

>
The FAQ for this group does not cover this exact situation, but it
does cover a similar one with a very similar solution:
>
Q: If I have a char * variable pointing to the name of a function, how
can I call that function?
>
You can read the answer to this question here:
>

http://c-faq.com/misc/symtab.html

>
It should be quite easy to figure out how to modify this to print the
values of various objects of the same type.
>

The solution should work even for structure variables.

>
You can use this technique to do that as well, it just takes more work
on your part.
>

thanks

>
--
Jack Klein
Home:http://JK-Technology.Com
FAQs for
comp.lang.chttp ://c-faq.com/
comp.lang.c++http://www.parashift.com/c++-faq-lite/
alt.comp.lang.l earn.c-c++http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html

The FAQ says that the program should maintain it's own symbol table
mapping all the variable-names to actual variables. If the program is
very
big having thousands of variables this doesn't scale well.

Is there any simple way of doing this. Though not simple, GDB has this
kind of
mechanism right? If my program has been compiled with GDB symbols in
it, can this
be done?

thanks

[Nate Eldredge]

Re: program should print it's own variables

sinbad <sinbad.sinbad@ gmail.comwrites :

The FAQ says that the program should maintain it's own symbol table
mapping all the variable-names to actual variables. If the program is
very
big having thousands of variables this doesn't scale well.
>
Is there any simple way of doing this. Though not simple, GDB has this
kind of
mechanism right? If my program has been compiled with GDB symbols in
it, can this
be done?

That's also in the FAQ, where it talks about the nlist function. Of
course this is not portable beyond some Unix flavors, and will not
work if your executable has been stripped. I don't think there is a
portable, reliable way to do this without listing all the variable
names in your source. (Of course, this could be automated with a
script of some kind.)

[Malcolm McLean]

Re: program should print it's own variables


"sinbad" <sinbad.sinbad@ gmail.comwrote

>The FAQ says that the program should maintain it's own symbol table
>mapping all the variable-names to actual variables. If the program is
>very big having thousands of variables this doesn't scale well.
>
>Is there any simple way of doing this. Though not simple, GDB has this
kind of mechanism right? If my program has been compiled with GDB
symbols in it, can this be done?
>

The short answer is that C doesn't allow you to do what you want. In this it
is unlike some other languages such as Lisp, which keep symbols at runtime.

However often the symbols haven't been stripped from the executable. So if
you know the structure of the executable it might be possible to work to the
variable in memory. However there are all sorts of issues with optimisations
and dynamic memory that make this non-trivial. It is also
compiler-dependent. It's not something you can knock up as a quick debugging
aid.

--
Free games and programming goodies.

http://www.personal.leeds.ac.uk/~bgy1mm