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c++ fundamentals question

I can do this:

double *emp;
emp = new double(10); //creates a ten element array on the heap, stores the address in emp

emp[0] = 1.11111;
emp[1] = 2.22222;
emp[2] = 3.33333;
emp[3] = 4.44444;

cout<<emp[0]<<" "<<
emp[1]<<" "<<
emp[2]<<" "<<
emp[3]<<endl;

With no problems, but if I try it with a struct:
struct EmpRec {
int ID;
char *firstname;
char *lastname;
};

EmpRec *e2;
e2 = new EmpRec(10);

I get the error:
"Cannot convert int to EmpRec in function main" (I'm using the Borland 4.5 compiler).

There must be something fundamental that I missing. Can anyone help?

Thanks,

Tom

mirec

double *emp;
emp = new double[10]; //creates a ten element array on the heap, stores the address in emp

emp[0] = 1.11111;
emp[1] = 2.22222;
emp[2] = 3.33333;
emp[3] = 4.44444;

//With no problems, but if I try it with a struct:
struct EmpRec {
int ID;
char *firstname;
char *lastname;
};

EmpRec *e2;
e2 = new EmpRec[10];

m.

mirec

double *xemp;
xemp = new double(100.2); //creates a double element and initialises to 100.2

To create array it's necessary to use [] brackets...
m.

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mirec

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tom419

ASKER

Ok sounds good. I can see the problem. I actually had code for a class that I had typed in wrong, which is why I used the parens instead of the []. So the () allow for initialization? I didn't know that, but I can see that it works
Thanks for your help,

Tom

tom419

ASKER

Very clear answer, and fast too!

Thanks!

udia

Hi,

when you write:
e2 = new EmpRec(10);

you are creating a new EmpRec and calling a ctor with a value of 10.

Since you do not have such a ctor, the compiler checks if there is an acceptable conversion that can be substituded.
The only available ctor is the compiler generated copy ctor which accepts an EmpRec&. This is how you get the error message (when the compiler tries to convert 10 to EmpRec).

The code:
double *emp;
emp = new double(10);
emp[0]..
emp[1]..

is actually a memory error, you are accessing unallocated memory using array notation.
As mirec wrote, the code should be:

emp = new double[10];

Udi.