How can I create an array of class objects whose constructor require few arguments?

Question

I've read about solution const A a[3] = { {0,0}, {1,1}, {2,2} }, but in my program const can't be used:

class Paper: public PaperQueue{  
  ...
  protected:
    typedef int (Utils::*funcPtr) (int, int); //I use external function there
    funcPtr p;                               
    Utils* fptr; 
  public:
    int pricefunc(){     
      addprice = (fptr->*p) (t,price);
    }

    Paper(int n, unsigned int pr):PaperQueue(n){         
       ...
       p=&Utils::commonpricefunc;    
    }
    void Put(int a){ 
       ...
    }
  ...
}    

class Bank{ 
  ...
  void Buy(Paper &p){
   (/*this function modifies many parameters in 'p'*/)
  ...
  }
  ...
}

int main(){
Bank B;    
int pn=5;
/* ? */ const Paper p[pn] = {{5,15},{5,15},{5,15},{5,15},{5,15}}; /* ? */
int paperloop=0;
...
p[paperloop].Put(p[paperloop].addprice);
B.Buy(p[paperloop]);
...

That gives me a LOT of errors(with pricefunc(),Put(),Buy(),...), or just "variable-sized object ‘p’ may not be initialized". Is there any way to make this array work? (Everything works fine if not to pass any parameters to constructor!)

I need to create an array, something like Paper (p[pn])(5,25) or something... Every constructor should receive these parameters and p[i] shouldn't be read-only object. — Slowpoke
– Slowpoke, Commented Nov 23, 2012 at 4:30

user1610015 · Accepted Answer · 2012-11-23 04:54:10Z

3

You can't use initializer lists for classes (non-PODs) because that would bypass the call to the constructor. You'll have to change it to a POD or use std::vector in the following ways:

If the class is copyable, as it appears to be, you can create a std::vector and fill it with the values you want:

const vector<Paper> papers(5, Paper(5, 15));

If you want to initialize it with different values, you can use an initializer list, but this is only supported in C++11:

const vector<Paper> papers = {Paper(1, 1), Paper(2, 2)};

Without C++11, you'll have to add the elements one by one, but then you can't make the vector const:

vector<Paper> papers;
papers.push_back(Paper(1, 1));
papers.push_back(Paper(2, 2));

answered Nov 23, 2012 at 4:54

user1610015

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1 Comment

Slowpoke Over a year ago

Thank you! int pn=5; vector<Paper> p(pn, Paper(5, 15)); did it. At least something.

Jeffmagma · Accepted Answer · 2018-07-23 19:33:56Z

0

Please check the code below, it can be compiled:

class Paper {
public:
    int x, y;
}; 

int main() {
    Paper p[5] = {{5,15}, {5,15}, {5,15}, {5,15}, {5,15}};
}

Please refer this post for more details, I think it explains very well

edited Jul 23, 2018 at 19:33

Jeffmagma

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answered Nov 23, 2012 at 4:35

Matt

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3 Comments

Slowpoke Over a year ago

Code complies fine on g++ 4.6.3, but in my program {5,15} are the parameters that I try to pass to the constructor.

Slowpoke Over a year ago

Ok, thank you ! When I wrote p[5] it seemed to work with warnings 'warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x '

Slowpoke Over a year ago

Is there any possibility to make it prettier? I wished to have something like p[n]...

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