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DATE 2010-03-01

HANGOUT

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Key: Value:

Key: Value:

MESSAGE
DATE 2010-03-21
FROM Ruben Safir
SUBJECT Re: [NYLXS - HANGOUT] C++ Workshop - Syntax Basics -- functions

Function Arguments:

We have already noted that the general rule for the input of functions
is the argument, or parameter list within the call operator.
furthermore, the default rule is that data in variables is copied into
the function body, creating a new set of data that is local to the scope
of the function. And we also stated that there is important exceptions
to this rule.

If you want to affect data that exists outside of your function, there
are several important methods to do so. The most basic method is the
use of pointers. When a pointer is defined in a scope global to the
your function, and when there is a value attached, memory is allocated
outside your function for the data and that can be manipulated within
the scope of your function. Data that is created within your function,
even if assigned to a pointer, still remains within your function only,
and disappears when the return value is only the pointer and when your
function instance ends. Let us look at this behavior.


_______________________________________________________________________

#include
using namespace std;

int global_a, * ptr_a;
int scope_data(int);
int * scope_pointer(int *);

int scope_data(int in){
in = 1000;
int out = 25;
return out;
}


int * scope_pointer(int *in){
*in = 1000;
int * out;
int buf = 25;
out = &buf;
cout << "The value of 'out' within function scope_pointer ==> "
<< *out << endl;
return out;
}

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

int func_return, *func_ptr_return;
global_a = 5;
ptr_a = &global_a;

func_return = scope_data(global_a);
cout << "global_a ==>" << global_a << endl;
cout << "ptr_a value==>" << *ptr_a << endl;
cout << "function return ==>" << func_return << endl;

func_ptr_return = scope_pointer(ptr_a);
cout << "\n\nPointer Behavior\n";
cout << "ptr_a value: Since ptr_a points to global_a, the memory
\
\nsegment is retained with the new value ==> " << *ptr_a
<< endl;
cout << "\n\nFunction ptr return value:meaningless garbage \
\nsince buf is out of scope ==> " << *func_ptr_return << endl
<



return 0;
}


_____________________________________________________________________________

ruben-at-www2:~/cplus/functions> g++ -Wall function_scope.cpp -o scope.bin
ruben-at-www2:~/cplus/functions> ./scope.bin
global_a ==>5
ptr_a value==>5
function return ==>25
The value of 'out' within function scope_pointer ==> 25


Pointer Behavior
ptr_a value: Since ptr_a points to global_a, the memory
segment is retained with the new value ==> 1000


Function ptr return value:meaningless garbage
since buf is out of scope ==> 108




  1. 2010-03-01 Paul Robert Marino <prmarino1-at-gmail.com> Re: [NYLXS - HANGOUT] this should not get through
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  3. 2010-03-02 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] [ruben-at-mrbrklyn.com: [jim-at-well.com: [conspire] open source
  4. 2010-03-02 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] Phone Tech Wars
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  6. 2010-03-02 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] this should not get through
  7. 2010-03-02 Paul Robert Marino <prmarino1-at-gmail.com> Re: [NYLXS - HANGOUT] this should not get through
  8. 2010-03-02 Paul Robert Marino <prmarino1-at-gmail.com> Re: [NYLXS - HANGOUT] this should not get through
  9. 2010-03-03 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics - agregate data types
  10. 2010-03-03 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics - agregate data
  11. 2010-03-03 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics - agregate data
  12. 2010-03-04 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics
  13. 2010-03-05 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics
  14. 2010-03-05 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] AlphaOne Labs invited you to the event "Ask-a-Sysadmin
  15. 2010-03-06 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] Professors Open Source Summer Experience -at-RIT
  16. 2010-03-07 Kevin Mark <kevin.mark-at-verizon.net> Re: [NYLXS - HANGOUT] Professors Open Source Summer Experience -at-RIT
  17. 2010-03-09 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics Structs Unions and
  18. 2010-03-09 From: "Beau Gould" <bg-at-capitalmarketsp.com> Subject: [NYLXS - HANGOUT] [JOB] System Administrator, NYC to 90k
  19. 2010-03-09 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] [JOB] System Administrator, NYC to 90k
  20. 2010-03-10 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] C++ Workshop _ Syntax Basics Structs Unions
  21. 2010-03-13 redpill <redpill-at-rcn.com> Subject: [NYLXS - HANGOUT] NYLXS Library?
  22. 2010-03-13 redpill <redpill-at-rcn.com> Subject: [NYLXS - HANGOUT] NYLXS Library?
  23. 2010-03-14 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] NYLXS Library?
  24. 2010-03-14 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] NYLXS Library?
  25. 2010-03-15 redpill <redpill-at-rcn.com> Re: [NYLXS - HANGOUT] NYLXS Library?
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  31. 2010-03-15 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] NYLXS Library?
  32. 2010-03-15 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] NYLXS Library?
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  36. 2010-03-16 redpill <redpill-at-rcn.com> Re: [NYLXS - HANGOUT] NYLXS Library?
  37. 2010-03-16 redpill <redpill-at-rcn.com> Re: [NYLXS - HANGOUT] NYLXS Library?
  38. 2010-03-17 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop - Switches and Break
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  41. 2010-03-21 Ruben Safir <mrbrklyn-at-panix.com> Subject: [NYLXS - HANGOUT] C++ Workshop - Syntax Basics -- functions
  42. 2010-03-21 Kevin Mark <kevin.mark-at-verizon.net> Re: [NYLXS - HANGOUT] C++ Workshop - Syntax Basics -- functions
  43. 2010-03-21 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] C++ Workshop - Syntax Basics -- functions
  44. 2010-03-21 Ruben Safir <mrbrklyn-at-panix.com> Re: [NYLXS - HANGOUT] C++ Workshop - Syntax Basics -- functions
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