Thread: Array of pointer variables....

Hello,

I'm starting to learn pointers...
i understand that :

Code:

...
int* p=new int [2];
for (int i=0; i<2; i++)
     cout<<(*(p+i)).beta;
...

But, I have trouble with array of pointer, something like this:

alpha[i] -> beta = 13.5
or (*alpha[i]).beta = 13.5

Could someone give an exemple of array of pointer?

>Could someone give an exemple of array of pointer variable?

Code:

#include <iostream>

int main ( void )
{
  static int a[5] = {1,2,3,4,5};
  int *pa[5] = {&a[0], &a[1], &a[2], &a[3], &a[4]};

  std::cout<<"Address: "<< &a[2] <<" Value: "<< a[2] <<std::endl;
  std::cout<<"Address: "<< pa[2] <<" Value: "<< *pa[2] <<std::endl;

  return 0;
}

-Prelude

>patPtrArray[3]->idNum = 6356;
Pointers have to point to a valid address before you can use them:

Code:

#include <iostream.h>

struct patientRec
{
  int idNum;
  int height;
  int weight;
};

int main()
{
  patientRec* patPtrArray[20];
  
  patPtrArray[3] = new patientRec;
  patPtrArray[3]->idNum = 6356;
  cout<<patPtrArray[3]->idNum;
  
  return 0;
}

-Prelude

all right lets go thru it line by line...

Code:

#include <iostream.h>

This is legal but poor form. You should be using the newer c++ style headers as the old iostreams library is deprecated.

Code:

struct patientRec
{
	int idNum;
	int height;
	int weight;
};

Again fine. Just a def for a struct.

Code:

int main()
{

This is good. We see a lot of void main here. That would have been bad but u didnt slip up there.

Code:

patientRec* patPtrArray[20];

You know what this line does?
It makes an uninitialised array of twenty pointers to a patientRec struct.

Code:

patPtrArray[3]->idNum = 6356;

Now what silly thing have you done here? Answer that and u have solved your problem. This says store 6356 in the int member idNum of the struct pointed to by patPtrArray[3]. But you remember that that array is UNINITIALISED.
What exactly are those pointers pointing at?
Where did you allocate anything other than pointers?

Code:

cout<<patPtrArray[3]->idNum;
	return 0;
}

This is good but std::cout and #include<iostream> would have been the order of the day.

Don't use #include <iostream.h> use #include <iostream> and using namespace std;

It would help if you told us the problem...

Edit:

Code:

patientRec* patPtrArray[3] = new patientRec;

That won't work... you have to initialise each element of the array.

Code:

patientRec* patPtrArray[3];
for( int i = 0; i < 3; i++ )
    patPtrArray[i] = new patientRec;

And you have to delete them all at the end of your program.

Code:

for( int i = 0; i < 3; i++ )
    delete patPtrArray[i];

Code:

#include <iostream.h>

Don't do that.

Code:

#include <iostream>
using namespace std;