Creating multiple objects and passing parameters through constructor

Question

I am trying to understand how to create multiple objects(20 in the current case) and pass parameter to the constructor as shown in the comments of the code. Unfortunately, I cannot pass parameters as well as have an array of objects at the same time.

I tried this as well to create the object convector con(100,200, construct(20)); but it didn't seem to give the desired result

#include <iostream>

class construct { 
public: 
    int a, b; 

    // Default Constructor 
    construct(int x1,int x2) 
    { 
         a = x1; 
         b = x2; 
    } 
    int getX1(){
        return a;
    }
    int getX2(){
        return b;
    }
};  
int main(){
    int p,q;
    construct* con = new construct[20](100,200);

for (unsigned int i = 0; i < 20; i++) {
    p=con[i]->getX1();
        q=con[i]->getX2();
        printf("%d %d \n",p,q);
    }
    delete con;
    return 1;
}

Expected result would be 20 objects created.

You should be using delete[] con to deallocate. std::vector is much easier to use. — Indiana Kernick
– Indiana Kernick, Commented Apr 23, 2019 at 6:13

Indiana Kernick · Accepted Answer · 2019-04-23 06:19:29Z

4

Just use std::vector. Seriously, there's no reason not to.

std::vector<construct> con(20, {100, 200});

answered Apr 23, 2019 at 6:19

Indiana Kernick

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2 Comments

StoryTeller - Unslander Monica Over a year ago

Upeed. Inb4 the OP comments with "my teacher at my university forbade the use of the standard library"

Indiana Kernick Over a year ago

@StoryTeller It really is unfortunate that some people have that attitude

robthebloke · Accepted Answer · 2019-04-23 06:14:22Z

-1

Yeah, for this you are likely to need placement new sadly (or use std::vector, and pass a newly constructed object as the second argument).

// call global new (effectively malloc, and will leave objects uninitialised)
construct* con = (construct*)::operator new (sizeof(construct) * 20);

// now call the ctor on each element using placement new
for(int i = 0; i < 20; ++i)
  new (con + i) construct(100, 200);

answered Apr 23, 2019 at 6:14

robthebloke

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2 Comments

Indiana Kernick Over a year ago

You're encouraging the use of raw memory management facilities

robthebloke Over a year ago

I did specify in my answer that using std::vector would be an option, but that isn't an answer to the actual question asked. The OP's question is about new. It's kinda hard to answer a question about raw memory management facilities, without you know, mentioning the raw memory management facilities.

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