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Quick Easy Pointer Question

Started by jrmiller84 10 replies 850+ views
Original Post
jrmiller84
jrmiller84
Hey guys, I'm working with linked lists for the 1st time and I think I'm pretty close to getting the animation system of my 2d scroller finished but am having a bit of trouble. The problem lies in the loop I made to find a specific item in the list. I need to test if the current item in the loop exists or not. I tried comparing it to NULL with an error "error C2065: 'NULL' : undeclared identifier." I also did some research and saw that someone recommended using Nullptr so I tried that and it didnt work as well, gave the same error. I understand the error and what it means just not sure of what to test it against to get what I'm looking for here. Here's my code, I'm sure this is a quick fix but I cant seem to find a good reference for the problem. 

FRAME_MASTER CFrames::Retrieve(int Action) {

	FRAME_MASTER *Current = Last_Frame;

	int x = 0;

	for(x=0;(x<Frame_Directives && Current != NULL && Current->Action != Action); x++) {

		Current = Current->Next;

	}

	return *Current;

}
I will forever be a student.
TEUTON
TEUTON
There is no reason why NULL should not work...

Try only writing
(xAction != Action)
Nice Coder
Nice Coder
instead of (xAction != Action)

Try

((((xAction != Action))

hth
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jrmiller84
jrmiller84
Yeah, I actually tried that first knowing that it should really be the same thing. When I do that, I don't get an error, it compiles and starts to run, then it gets an access violation error at runtime. Only thing I can think of is that maybe its going out of its bounds?
I will forever be a student.
jrmiller84
jrmiller84
It seems that just using Current as the arguement works. Now the access violation problem seems to be related to the last clause of that line of statements: Current->Action != Action. It seems I may not be linking the lists together correctly. This seems to be a pretty confusing concept.
I will forever be a student.
jrmiller84
jrmiller84
Wow, I realized what my problem was. I was redefining the previous frame structure everytime I added a new item onto the list. So it always had a null previous structure! I'm an idiot but... as I always say about programming when you figure out what you've done wrong it's a very rewarding activity. As soon as I fixed that error, it compiled and low and behold... had Megaman running on my screen. Thanks guys!
I will forever be a student.
Will F
Will F
If you're using C++, why not use std::list, rather than writing your own linked list? The C++ FAQ Lite has a section explaining why you should use the standard library's container classes. If you aren't comfortable using std::list here is a good Standard Library tutorial.

Here's a short code sample showing how to determine if something exists in a list

#include <list>#include <algorithm>#include <iostream>int main(){        std::list<int> foo;        foo.push_back(5);        std::list<int>::iterator itor;        itor = std::find(foo.begin(), foo.end(), 5);        if ( itor != foo.end() )                std::cout << "5 was found\n";        itor = std::find(foo.begin(), foo.end(), 7);        if ( itor == foo.end() )                std::cout << "7 was not found\n";}


It will output:
5 was found7 was not found

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