Creating array of objects - No default constructor (needs initializer list)

This is a question regarding creating array of objects using new.
This class doesnt have default constructor, i.e., should provide a initializer list.

Ex.
Class CTest
{
private:
int m_nIndex;
long m_lLongIndex;

public:
CTest(int nIndex, long lLongIndex); //No default constructor
}

CTest:: CTest(int nIndex, long lLongIndex): m_nIndex(nIndex), m_lLongIndex(lLongIndex)
{

}

void main(void)
{
CTest* ptrTest = new CTest[5] ??????????
// How to do this?
}


Thanks and Regards
Kannan S CTest* ptrTest = new CTest[5] ??????????

Your stuck, since operator new[] requires your class to have a default constructor.

Why not just create a default constructor, and set the appropriate member variables to reasonable defaults?

Regards,

Paul McKenzie

Yes u r right. Because of new operator...
I cannot have a default constructor, because of design issues.

One cannot create an object of the class i am creating without supplying the necessary parameter to construct and object.

Without those parameters the object is meaningless.

So i have to do this way.

Is it possible to do this?

Wild guess - using operator overloading or something like that...?

Quote:

---

Without those parameters the object is meaningless.

---

So if it's meaningless, don't allow usage of it until the parameters are set correctly, either they are set through construction (as they are now) or a secondary Init( ) function. If the user tries to call a member function on the object that is not properly initialized, return an error code, throw an exception, something to indicate that the object is in an invalid state.

As a live example, you can create an empty ifstream object, but it's useless unless the programmer calls the "open()" method, or constructs an ifstream with a file name parameter.

Regards,

Paul McKenzie

Another solution is to create a third constructor -- one that takes a structure of two integers. Then you can create a vector (which is much safer than "new") using the single argument constructor:

Code:

---

#include <vector>
#include <iostream>

struct IndexStruct
{ 
  IndexStruct(int i1, int i2) : index(i1), longindex(i2) { }
  int index;
  int longindex;
};

class CTest {
  public:
      CTest(const IndexStruct& IS) : m_nindex(IS.index),
          m_lLongIndex(IS.longindex) { }
      //....
      int m_nindex;
      int m_lLongIndex;
};


//...
using namespace std;

int main()
{
  // This creates 5 CTests, initialized with index = 1, and longindex = 2
  std::vector<CTest> CT(5,IndexStruct(1,2));
  //...
  for ( int i = 0; i < CT.size(); i++)
      cout << CT[i].m_index << " " << CT[i].m_lLongIndex << endl;
}

---

With vector, you eliminate the calls to new and delete, and you can initialize the vector with a single value. The value in the above case is a reference to the IndexStruct structure.

Regards,

Paul McKenzie

Try first creating a pointer array, and then filling each item in the array with via appropriate constructor.
Example:

int main(int, char*)
{
const int Max = 5;
CTest** ptrTest = new CTest*[5];
for(int i = 0;i < Max;++i) ptrTest[i] = new CTest(i, i*3);
return 0;
}

Thanks Axter
It works...

Thanks paul mc. for your suggestions.

Kannan

apply** ptrapply = new apply*[5];

for(int i = 0;i < Max ; ++i)
ptrapply[i] = new apply();

How do you access the information in the class through the pointer??

With the other example how would i access ctest info from main
or better yet in mine
how do i access the apply class through the pointers i made for each obj of apply??

If i am not wrong...

---> apply** ptrapply = new apply*[5];

Creating array of pointers, each of type apply.
i.e., creting an array of size 5, each element is a pointer to apply object.

--->for(int i = 0;i < Max ; ++i)
--->ptrapply[i] = new apply();

Then allocating memory for each arry element with new.

Thanks
Kannan

now how do i access the information in class apply???

Quote:

---

now how do i access the information in class apply???

---

Code:

---

ptrapply[i]->member = xxx;

---

ptrapply[i]->askname();

what do i make this equal to???

also if askname is in the base class and apply is derived from the base class how do i access the information

Hope this answers your questions...


#include <iostream>
using namespace std;

class CBaseTest
{
public:
int m_ba;
int m_bb;
CBaseTest(int a, int b) : m_ba(a), m_bb(b)
{
}

void ShowMessage(char* szMsg)
{
cout<<endl<<szMsg<<endl;
}
};

class CTest : public CBaseTest
{

public:
int m_a;
int m_b;

CTest(int a, int b);
~CTest() {}
};

CTest::CTest(int a, int b) : CBaseTest(a, b), m_a(a), m_b(b)
{
}

int main (void)
{
const int Max = 5;
CTest** ptrTest = new CTest*[Max];

for(int i = 0;i < Max;++i)
{
ptrTest[i] = new CTest(i, i*3);
cout<<endl<<ptrTest[i]->m_a<<"\t"
<<ptrTest[i]->m_b<<"\t"
<<ptrTest[i]->m_ba<<"\t"
<<ptrTest[i]->m_bb<<endl;
}
ptrTest[i]->ShowMessage("Will this be displayed???");

return 0;
}

Thanks and Regards
Kannan S