I’m following the wiki entry about OOP and I got it working, the problems raise when I want to access a variable OUTSIDE the scope of the object.
For example this code in testApp setup():
n=1;
balls= new ofBall*[n];
for(int i=0;i<n;i++){
balls[i]=new ofBall(ofRandom(0,ofGetWidth()),ofRandom(0,ofGetHeight()),ofRandom(1,100));
}
and this code in Ball constructor:
r = _r;
x = _x;
y = _y;
vx = ofRandom(-1,1);
vy = ofRandom(-1,1);
int tempGrayValue=10+ofRandom(0,245);
red=green=blue=tempGrayValue;
printf("\ntestApp var accessed from ball:%i",n);
I receive this as a result: error: ‘n’ was not declared in this scope
i don’t really know/understand what you want to accomplish, but i try to guess.
please try to provide the signature and scopes of your(member-) functions,
so we can help you more easily.
i guess, first you want to dynamically allocate an array ofBall-objects
and set the values. an easy approach would be
void somefunc
{
//...
int n = 1;
ofBall* balls = new ofBall[n]; //now you have n instances of ofBall and n calls to the default constructor
//should check/be prepared for out-of-memory-situations
for (int i = 0; i < n; ++i)
{
balls[i]->SetValues(ofRandom(0,ofGetWidth()),ofRandom(0,ofGetHeight()),ofRandom(1,100));
}
//...
}
you don’t need a default constructor because the compiler will generate one,
but it is good practice since only then you can initialize all values.
then implement a “SetValues” function so you can set the values afterwards.
i don’t know why want to access “n” in ofBall (ctor or whereever) - it doesn’t make sense. why should a ball object know that it is the 1st, 2nd, 3rd, … ball?
if you want to have unique ids, then try static counters and an id member variable.
and of course the compiler screams. n is not in the scope of the constructor.
Sorry, yesterday was a tough one and my question was not clear enough.
Basically I want to access a public variable in TestApp from inside an object.
example:
in testApp.h:
class testApp : public ofSimpleApp{
public:
int testAppVar;
}
in testApp.cpp:
void testApp::setup(){
testAppVar=12345;
}
in the Ball constructor:
printf("\n testAppVar var accessed from inside ball:%i",testAppVar);
I’m trying this because in Processing is always possible to access a public variable in PApplet from an object instantiated inside the PApplet setup(), while in OF it seems to be a bit different.
in Processing I would do this way:
int PAppletVar;
Ball b;
void setup(){
PAppletVar=12345;
b=new Ball();
}
void draw(){
}
class Ball{
Ball(){
println("PApplet var accessed from inside Ball:"+PAppletVar);
}
}
getting this as a result:
_
PApplet var accessed from inside Ball:12345_
I tend to put things I need to access from several objects into a singleton and then have the objects get an instance of that to read vars from, possibly not the best solution, but it works and I use it all the time.
I’m pretty sure I got the gist of that code from www.gamedev.net in the first place, was trying to find it so I could link to it to provide credit, context and I’m sure there would be a discussion on the site to go with it as well, but wasn’t able to find it.
Will edit this post if I remember when it came from.
inner classes do have access to their parent classes functions and methods, where as pure classes don’t. To do pure classes in p5, when you add a tab, use .java not .pde as the extension.
i went through the example with “AGlobalVideoImageData” from above but as a total beginner i had some troubles, so after a while i figured it out, but i thought it might be helpfull to post this example with “where to put what” as well:
// testApp.cpp
//-------------------------------------
#include "testApp.h"
void testApp::setup(){
//Singleton *testinst = Singleton::Instance();
testinst = Singleton::Instance();
std::cout << "testvalue-----------------------(" << testinst->testVal << ")\n\n";
testinst->testVal =100;
std::cout << "testvalue-----------------------(" << testinst->testVal << ")\n\n";
}
// testApp.h
//-------------------------------------
#ifndef _TEST_APP
#define _TEST_APP
#include "ofMain.h"
#include "Singleton.h"
class testApp : public ofSimpleApp{
public:
void setup();
void update();
void draw();
void keyPressed(int key);
void keyReleased(int key);
void mouseMoved(int x, int y );
void mouseDragged(int x, int y, int button);
void mousePressed(int x, int y, int button);
void mouseReleased();
Singleton *testinst;
};
#endif
// Singleton.h
//-------------------------------------
#ifndef _SINGLETON
#define _SINGLETON
#include "ofMain.h"
// Declaration
class Singleton {
public:
static Singleton* Instance(); // pointer to itself
int testVal;
protected:
Singleton(); // protected constuctor
private:
static Singleton* _instance;
};
#endif
// Singleton.cpp
//-------------------------------------
#include "Singleton.h"
// Implementation
Singleton* Singleton::_instance = NULL;
Singleton* Singleton::Instance() {
// checks if instance already exists:
if (_instance == NULL) {
_instance = new Singleton;
}
return _instance;
// from OF forum:
/*
static Singleton inst;
return &inst;
*/
}
Singleton::Singleton() // constructor
{
testVal = 20;
}
everytime i need to access a variable that lives inside some object i create a pointer to that object and use it as a reference. and when inside a class and want to pass that as a reference you can use the comand “this”. so for example in your code you could do it like this:
n=1;
balls= new ofBall*[n];
for(int i=0;i<n;i++){
balls[i]=new ofBall(ofRandom(0,ofGetWidth()),ofRandom(0,ofGetHeight()),ofRandom(1,100), this); //"this" returns a pointer to the testApp object
}
and in your ball constructor
testApp * testAppPointer;
ofBall::ofBall(/*your other variables...*/, testApp *_testAppPointer){
//your other variables...
testAppPointer = _testAppPointer;
printf("\ntestApp var accessed from ball:%i", testAppPointer->n);
}
this was all from the top of my head but hope it works.
