How to set individual class array elements using class methods?

Question

I'm using C++ and am trying to set an array element values with a setter method. The array is a class private member:

class Boo{
  private:
     int *x;
  public:
     Boo();
     ~Boo();

     void setX(int,int);
     int getX(int);
}

Boo::Boo(){

  x = new int[1];
  x = 0;
}

void Boo::setX(int value, int index){
      //set condition for NULL 
      x[index] = value;
}

int Boo::getX(int index){

    if(x[index] == NULL) {cout<<"invalid index"<<end; return;}
    return x[index];
}

void test(){
    Boo *p = new Boo();

    p->setX(12,0);
    cout<<p->getX(0)<<endl;
}

I been trying to test setting the values in 'x' starting with index '0' (like test()) but it crashes. I wanted to write a program where I run a loop counting up, and I set the array values. Can this be accomplish this way?

it crashes because x is set to null after you allocated it. stop by learncpp.com and see what they got to offer — DevGuy
– DevGuy, Commented Oct 7, 2016 at 3:41
I'm guessing the crash has something to do with the fact that you are setting the pointer x to 0 in your constructor, so then when you try to access the 0-th index in setX() you're trying to access an element that doesnt exist for x which gives you undefined behavior (or possibly a seg fault). — Jvinniec
– Jvinniec, Commented Oct 7, 2016 at 3:44

yumetodo · Accepted Answer · 2016-10-07 03:48:27Z

Do not use new in C++!

In this case, you should use std::vector<int>.

If you want to fix your code unless use std::vector,

#include <cstddef>
#include <iostream>
#include <stdexcept>
#include <memory>
using std::size_t;

class Boo {
private:
    int *x;
    size_t size;
    size_t capacity;
public:
    Boo();
    ~Boo();
    void setX(int,size_t);
    int getX(size_t);
};
Boo::Boo() : size(), capacity(1) {
    this->x = new int[1];
    //x = 0;//DO NOT ASSIGN NULL POINTER!!!!
}
Boo::~Boo() noexcept {
    delete[] x;
}
void Boo::setX(int value, size_t index){
    if(this->capacity <= index) throw std::out_of_range("Boo::setX");//YOU MUST CHECK RANGE
    this->x[index] = value;
    ++this->size;
}

int Boo::getX(size_t index){
    if(this->size <= index) throw std::out_of_range("Boo::getX");//YOU MUST CHECK RANGE
    return x[index];
}

void test(){
    auto p = std::make_unique<Boo>();
    p->setX(12,0);
    std::cout << p->getX(0) << std::endl;
}
int main(){
    test();
}

http://melpon.org/wandbox/permlink/aIhwC5c9o1q8ygIo

Rahul Singh · Accepted Answer · 2016-10-07 03:43:45Z

0

Boo::Boo()
{
    x = new int[1];
    x = 0;
}

you are not able to set value in an array because after initializing with memory, you have set the pointer of an array to null in constructor.

please use x[0] = 0; instead of x = 0;

answered Oct 7, 2016 at 3:43

Rahul Singh

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