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Access reading error when using class member variable


Access reading error when using class member variable

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Access reading error when using class member variable
Tag : cpp , By : Ian Badcoe
Date : January 02 2021, 06:48 AM


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Accessing a member variable's address in derived class.Behavior change when member is having different access specifier


Tag : cpp , By : shehan
Date : March 29 2020, 07:55 AM
may help you . Short answer: There is no undefined behavior involved. The behavior you see is:
The expression &A::a is an attempt to obtain a pointer to member pointing to member a of class A. If a is protected in A, this expression only passes access checks within class A (or friends of A). In a class B derived from A, you can get the same pointer to member only via the expression &B::a (note that the type of this expression will still be int A::*). So: if A::a is protected in A, the expression &A::a is not allowed in a member function of derived class B. This is your compiler error. if A::a is public in A, this expression is valid, producing a pointer to memeber. Streaming a pointer to member to an ostream, for example using cout << &A::a will print 1. This results from invoking ostream::operator << (bool). You can use the boolalpha manipulator to see that this is indeed the chosen overload: cout << boolalpha << &A::a will print true. If you use the modified expression &(A::a) or simply &a, no pointer to member is formed. Here the address of member a of the current object (i.e the same as &(this->a)) is taken, which is a regular pointer to int. This access to a protected member of a base class subobject of *this is valid, so that variant can be used even if a is protected in A.

Javascript class member function calling member function by setInterval, couldn't access member variable


Tag : javascript , By : Viv
Date : March 29 2020, 07:55 AM
I hope this helps . setInterval() doesn't work with this. See here: https://developer.mozilla.org/en-US/docs/Web/API/WindowTimers/setInterval#The_this_problem
function job_queue(){
    this.job = null;
    this.pointer = this.job;
    this.job_dispatcher = null; 
    this.length = 0;
}
job_queue.prototype.add_job = function( job ){
    if( this.job == null ){
        console.log('1st');
        this.job = {
            job:job,
            next:null
        };
        this.pointer = this.job;
        this.length = 1;
    }else{
        console.log('2nd');
        this.pointer.next = { 
            job:job,
            next:null
        };
        this.pointer = this.pointer.next;
        this.length++;
    }
};

job_queue.prototype.event_handler = function(){
        
        if( typeof this.job['job'] == 'undefined'){
            console.log('??');
        }
        if( this.job.job != null ){
            console.log('hi');
            this.job.job();
            this.job = this.job.next();
        }

}

job_queue.prototype.start_dispatch = function(){
    var self = this;
    if( this.job_dispatcher == null ){
        console.log( this.event_handler );
        this.job_dispatcher = setInterval( function(){self.event_handler()},1000);
    }
}



var jq = new job_queue();
function a(){
    console.log('hi');
};
function b(){
    console.log('hi2');
}
jq.add_job(a);
jq.add_job(b);
jq.add_job(a);
jq.start_dispatch();

Error when using public member function to access private member variable: Variable "was not declared in this scope


Tag : cpp , By : user123585
Date : March 29 2020, 07:55 AM
wish helps you Update for anyone having trouble returning multidimensional arrays , You forgot the Card::
int (*Card::palette())[3]{
    return _palette;
}
class Card {
private:
    static int  _palette[][3];
public:
    static int  (*palette())[3];
};

Access a member function of an object that is a member variable of a parent class


Tag : php , By : rhyhann
Date : March 29 2020, 07:55 AM
This might help you Dont instantiate a seperate parent class, it will be instantiated as part of instantiating the child class.
Also pass the object to the child instantiation and create a __construct() method and pass the parameter on to it.
class Child extends Parent
{
    public __construct($var)
    {
        parent::__construct($var);
    }

    public function doStuff()
    {
        return parent::$object->objectFunction());
    }

}
public function control()
{
    //$parent = new Parent(new Object($variable));

    $child = new Child(new Object($variable)); // line 25
    $child->doStuff();
}

How can I access member variables of a vector of objects that is a member variable from a class?


Tag : cpp , By : Mena
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I do know how to access member variables given a vector of objects but suppose
float value = n.getnn()[i].getval()[j][k];
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