Programming Forums > Application Development > C++

CFlower · Nov 23rd, 2009, 12:04 AM

hi all ,
i have problem and three days just trying find out, but no result!!

i have two diffirent classes: Xnode and Ynode
in Ynode, i have method called tree() which it gets as argument - a reference of Xnode (as const) , and it calls its method to return one private variable xx.

(Toggle Plain Text)

void Ynode::tree(const Xnode& x){
       const Node* n=x.list();
       std::cout << n->value;
}
const  Node* Xnode::list() const {
         const Node* nod=xx;
         std:cout << nod->value;
         return nod;
}

the output inside Xnode was good value(as expected) , but the second (after return from list()) -was undefined value - ...56923434.
can you tell me what's wrong? why the pointer is undefined in
const Node* n=x.list(); ??

its little urgent!.

thanks a lot.

DaWei · Nov 23rd, 2009, 2:18 AM

Yep. You haven't learned about scope. You might want to Google it (disregard any links regarding mouthwash).

Incidentally, it isn't urgent. You might want to also Google Eric Raymond's "Smart Questions."

CFlower · Nov 23rd, 2009, 8:32 AM

hi,
Do you think i didnt try googling or learning before posting? i did.
but this kind of Q is not easy to solve and needs epecially assistance from others who can advise.

thanks anyway

Ancient Dragon · Nov 23rd, 2009, 9:20 AM

in list(), what is xx?

>>was undefined value - ...56923434.
That's not undefined value, but uninitialized value. undefined means you tried to use a variable that had not been declared. uninitialized means you used a variable that had been declared but not set to anything; it just contains whatever random data was in memory at the time the variable was declared.

DaWei · Nov 23rd, 2009, 12:19 PM

I gave you the correct term to Google. Here are the first two paragraphs from the first hit for C++ scope:

Quote:

C++ names can be used only in certain regions of a program. This area is called the "scope" of the name. Scope determines the "lifetime" of a name that does not denote an object of static extent. Scope also determines the visibility of a name, when class constructors and destructors are called, and when variables local to the scope are initialized. (For more information, see Constructors and Destructors.) There are five kinds of scope:

*

Local scope A name declared within a block is accessible only within that block and blocks enclosed by it, and only after the point of declaration. The names of formal arguments to a function in the scope of the outermost block of the function have local scope, as if they had been declared inside the block enclosing the function body. Consider the following code fragment:

This tells you that nod is only valid inside the function where it is defined.

Search is the first part. The second is the ability to read and comprehend. The are requirements for a good programmer because the time economy is important.

Nov 23rd, 2009, 12:04 AM	#1
CFlower Newbie Join Date: Nov 2009 Posts: 6 Rep Power: 0	Problem with pointer in function return hi all , i have problem and three days just trying find out, but no result!! i have two diffirent classes: Xnode and Ynode in Ynode, i have method called tree() which it gets as argument - a reference of Xnode (as const) , and it calls its method to return one private variable xx. (Toggle Plain Text) void Ynode::tree(const Xnode& x){ const Node* n=x.list(); std::cout << n->value; } const Node* Xnode::list() const { const Node* nod=xx; std:cout << nod->value; return nod; } void Ynode::tree(const Xnode& x){ const Node* n=x.list(); std::cout << n->value; } const Node* Xnode::list() const { const Node* nod=xx; std:cout << nod->value; return nod; } the output inside Xnode was good value(as expected) , but the second (after return from list()) -was undefined value - ...56923434. can you tell me what's wrong? why the pointer is undefined in const Node* n=x.list(); ?? its little urgent!. thanks a lot. Last edited by Ancient Dragon; Nov 23rd, 2009 at 5:31 AM. Reason: replaced icode tags with code tags

Nov 23rd, 2009, 2:18 AM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 7,021 Rep Power: 12	Re: Problem with pointer in function return Yep. You haven't learned about scope. You might want to Google it (disregard any links regarding mouthwash). Incidentally, it isn't urgent. You might want to also Google Eric Raymond's "Smart Questions." __________________ 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 Politically Incorrect

Nov 23rd, 2009, 8:32 AM	#3
CFlower Newbie Join Date: Nov 2009 Posts: 6 Rep Power: 0	Re: Problem with pointer in function return hi, Do you think i didnt try googling or learning before posting? i did. but this kind of Q is not easy to solve and needs epecially assistance from others who can advise. thanks anyway

Nov 23rd, 2009, 9:20 AM	#4
Ancient Dragon PFO God In Training Join Date: Jun 2005 Location: near St Louis, MO. (USA) Posts: 1,534 Rep Power: 6	Re: Problem with pointer in function return in list(), what is xx? >>was undefined value - ...56923434. That's not undefined value, but uninitialized value. undefined means you tried to use a variable that had not been declared. uninitialized means you used a variable that had been declared but not set to anything; it just contains whatever random data was in memory at the time the variable was declared. __________________ PFO's FAQ is here

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Programming Forums > Application Development > C++

Problem with pointer in function return