Programming Forums > Application Development > C

mguarin · Oct 27th, 2005, 2:25 AM

good day!

can anyone show me how access data of argc and argv if outside main(int argc, char *argv[])?

thnx u very much..

stevengs · Oct 27th, 2005, 5:00 AM

pass them as parameters to 'outside of main'.

grumpy · Oct 27th, 2005, 5:03 AM

....or copy them somewhere so they can be accessed globally .....

stevengs · Oct 27th, 2005, 5:10 AM

merci Monsieur grumpy

my answer was unacceptably incomplete as it stood.

jim mcnamara · Oct 27th, 2005, 11:24 AM

(Toggle Plain Text)

#include <stdlib.h>
char **argvptr=NULL;
int    *argcptr=NULL;

int main(int argc, char **argv)
{
     argcptr=&argc;
     argvptr=argv;
     /* now you can reference them as argcptr and argvptr in any function */
     return 0;
}

grumpy · Oct 28th, 2005, 7:12 AM

I fail to see the point of storing a pointer to argc rather than just its value.

DaWei · Oct 28th, 2005, 8:40 AM

Mguarin, are you the type that ignores things you hear that you don't like? This looks suspiciously like part of your other thread. Stack access is implicit in most implementations of the language. It isn't something you do directly or need to do directly. That fact hasn't changed since I posted it, like it or not.

jim mcnamara · Oct 28th, 2005, 10:53 AM

Quote:

Originally Posted by grumpy

I fail to see the point of storing a pointer to argc rather than just its value.

The whole concept is not a good one. OP wants direct access to the "stack", only he doesn't understand how stacks work in C.

What I think he wants is access to arc and argv everywhere, which sounds like a design problem to me. Probably he doesn't know about getopt() or whatever passes for function that in Windows.

DaWei · Oct 28th, 2005, 11:18 AM

Actually, it begins like this:

Quote:

and is it possible to access content of int argc and char * argv[] to other function like sample blue(int argc, char *argv[])?

Even using the word, "stack", in my reply, was obviously a bad call on my part.

Quote:

Argc and argv are values pushed onto the stack by the entry code when main is called. There is nothing magic about them or their names, it's a convention. Putting those labels as arguments for another function will not make them magically appear there. When you write the call to the second function, the compiler will require of you that you supply arguments with the call, just as always.

argv is an array of character pointers. Use atoi on the values pointed to by the contents of each element, just as you would with any other array of the same type. Bear in mind that the thangys to be converted need to be validly convertible.

grumpy · Oct 28th, 2005, 9:38 PM

Oh ..... Okaaay.

I hadn't picked up that this was a continuation of another thread.

The "stack" is an implementation detail associated with a compiler and the machine you're running on. It is also a term used sometimes by C programmers to refer to the place where memory for local variables exist (as opposed to the "heap" or something similar, which is the place where dynamically memory is accessed from). The history of the terms "stack" and "heap" are historical: on some machines a decade or so ago, stack and heap were physically implemented as different banks of memory chips. Dawei's reference to the stack for passing arguments to functions dates back to that type of machine: compilers passed arguments to functions by copying their values to the stack.

With modern compilers, operating systems and computer hardware, the distinction between "stack" and "heap" is meaningless - physically, there is rarely any distinction made between different types of memory, even if programmers use antiquated terms like "heap" and "stack" to understand differences between mechanisms to access memory.

Trying to access the "stack" in any way is meaningless --- particularly on machines that don't have a stack. Even if you can, them mechanisms are highly specific to compiler and operating system.

With access to arguments of main(int argc, char **argv), there is no point in trying to access the "stack" in which the arguments (argc and argv) exist. The compiler takes care of that for you, and every compiler does it differently. With modern compilers, there may even be no stack to access. If you want to access those values, the way you do it is to access the arguments within main, and copy their values elsewhere, as described by stevengs and myself (with an example of sorts by jim). The C standard requires compilers to provide you the ability to access command line arguments like this, but leaves it up to compiler vendors as to how they implement it.

And, if you are somehow looking for a means of intercepting argc and argv before a program sees them --- forget it. If you had a genuine and useful reason for doing that, you would already know how. The ONLY reasons I can think of to want to do such things are malicious and childish (eg writing a virus).

Oct 27th, 2005, 2:25 AM	#1
mguarin Newbie Join Date: Oct 2005 Posts: 18 Rep Power: 0	STACK- acessing argc and argv outside main() good day! can anyone show me how access data of argc and argv if outside main(int argc, char *argv[])? thnx u very much..

Oct 27th, 2005, 5:00 AM	#2
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	pass them as parameters to 'outside of main'. __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty

Oct 27th, 2005, 5:10 AM	#4
stevengs Professional Programmer Join Date: May 2005 Location: Bad Nauheim, Germany Posts: 436 Rep Power: 4	merci Monsieur grumpy my answer was unacceptably incomplete as it stood. __________________ -Steven "Is this a piece of your brain?" - Basil Fawlty

Oct 27th, 2005, 11:24 AM	#5
jim mcnamara Hobbyist Programmer Join Date: Jun 2005 Location: New Mexico Posts: 228 Rep Power: 4	(Toggle Plain Text) #include <stdlib.h> char *argvptr=NULL; int argcptr=NULL; int main(int argc, char *argv) { argcptr=&argc; argvptr=argv; / now you can reference them as argcptr and argvptr in any function / return 0; } #include <stdlib.h> char argvptr=NULL; int argcptr=NULL; int main(int argc, char *argv) { argcptr=&argc; argvptr=argv; / now you can reference them as argcptr and argvptr in any function */ return 0; }

Oct 28th, 2005, 8:40 AM	#7
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Mguarin, are you the type that ignores things you hear that you don't like? This looks suspiciously like part of your other thread. Stack access is implicit in most implementations of the language. It isn't something you do directly or need to do directly. That fact hasn't changed since I posted it, like it or not. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Oct 27th, 2005, 5:03 AM	#3
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	....or copy them somewhere so they can be accessed globally .....

Oct 28th, 2005, 7:12 AM	#6
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	I fail to see the point of storing a pointer to argc rather than just its value.

Oct 28th, 2005, 9:38 PM	#10
grumpy Programming Guru Join Date: Jun 2005 Location: Adelaide, South Australia Posts: 1,260 Rep Power: 5	Oh ..... Okaaay. I hadn't picked up that this was a continuation of another thread. The "stack" is an implementation detail associated with a compiler and the machine you're running on. It is also a term used sometimes by C programmers to refer to the place where memory for local variables exist (as opposed to the "heap" or something similar, which is the place where dynamically memory is accessed from). The history of the terms "stack" and "heap" are historical: on some machines a decade or so ago, stack and heap were physically implemented as different banks of memory chips. Dawei's reference to the stack for passing arguments to functions dates back to that type of machine: compilers passed arguments to functions by copying their values to the stack. With modern compilers, operating systems and computer hardware, the distinction between "stack" and "heap" is meaningless - physically, there is rarely any distinction made between different types of memory, even if programmers use antiquated terms like "heap" and "stack" to understand differences between mechanisms to access memory. Trying to access the "stack" in any way is meaningless --- particularly on machines that don't have a stack. Even if you can, them mechanisms are highly specific to compiler and operating system. With access to arguments of main(int argc, char **argv), there is no point in trying to access the "stack" in which the arguments (argc and argv) exist. The compiler takes care of that for you, and every compiler does it differently. With modern compilers, there may even be no stack to access. If you want to access those values, the way you do it is to access the arguments within main, and copy their values elsewhere, as described by stevengs and myself (with an example of sorts by jim). The C standard requires compilers to provide you the ability to access command line arguments like this, but leaves it up to compiler vendors as to how they implement it. And, if you are somehow looking for a means of intercepting argc and argv before a program sees them --- forget it. If you had a genuine and useful reason for doing that, you would already know how. The ONLY reasons I can think of to want to do such things are malicious and childish (eg writing a virus).

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Programming Forums > Application Development > C

STACK- acessing argc and argv outside main()