def copy ctor and member-arrays

[dmoos AT esigma-systems DOT de]

Hi all,

i've got a simple question: how does the default copy-constructor act
on member-arrays ? Since array-variables are often treated as pointers
to the array-element-type, one could think that the default copy-
constructor would just copy the address of the first element of the
member-array-variables.

A simple test-programm reveals, that g++-2.96 instead copies the
member-array array-element by array-element.

Please enlighten me on this topic.
Thanks in advance. Test-programm attached.

Darius.

#include <iostream>

class X {
int v[4];

public:
X *This;

X(int i1 = 0, int i2 = 0, int i3 = 0, int i4 = 0) { v[0] = i1; v[1] = i2; v[2] = i3; v[3] = i4; This = this; };
~X() {};

friend ostream& operator<< (ostream& s, const X& w) { return s << " " << w.v[0] << "[" << &w.v[0] << "] " << w.v[1] << " " << w.v[2] << " " << w.v[3]; };
};

int main(int argc, char **argv)
{
X v;
X w(1, 2, 3, 4);
X x(w);

std::cout << "v = (" << v << ")" << std::endl;
std::cout << "w = (" << w << ")" << " This = " << w.This << std::endl;
std::cout << "x = (" << x << ")" << " This = " << x.This << std::endl;
}
Output:
v = ( 0[0xbffffa20] 0 0 0)
w = ( 1[0xbffffa00] 2 3 4) This = 0xbffffa00
x = ( 1[0xbffff9e0] 2 3 4) This = 0xbffffa00

[Karl Heinz Buchegger]

dmoos AT esigma-systems DOT de wrote:

Hi all,

i've got a simple question: how does the default copy-constructor act
on member-arrays ? Since array-variables are often treated as pointers
to the array-element-type, one could think that the default copy-
constructor would just copy the address of the first element of the
member-array-variables.
There is a misconception on your part:

Arrays are not pointers !

Only in certain circumstances, eg. when passing an array to
a function, the array decays into a pointer to its first
element.

But: Arrays are not pointers !

A simple test-programm reveals, that g++-2.96 instead copies the
member-array array-element by array-element.

As it should do it.

--
Karl Heinz Buchegger
kb******@gascad .at

[DaKoadMunky]

Is it possible to initialize elements of a member array in the member
initializer list?

The reason I ask is because I defined a class X. I then defined a class
ArrayOfX which contains an array of X.

When relying on the compiler generated copy constructor for ArrayOfX the X copy
constructor was called for each element in the array of X held by the ArrayOfX
instance.

However, when I provided a copy constructor for ArrayOfX the default
constructor for each X element in the array was called.

I know how to use the member initializer list to specify construction methods
for individual objects. Can it also be used to initialize array elements?

I am unware of the syntax if it can be.

Regards
Brian F. Seaberg
Naperville, Illinois
Delray Beach, Florida

[Victor Bazarov]

"DaKoadMunk y" <da*********@ao l.com> wrote...

Is it possible to initialize elements of a member array in the member
initializer list?
No.
The reason I ask is because I defined a class X. I then defined a class
ArrayOfX which contains an array of X.

When relying on the compiler generated copy constructor for ArrayOfX the X copy constructor was called for each element in the array of X held by the ArrayOfX instance.

However, when I provided a copy constructor for ArrayOfX the default
constructor for each X element in the array was called.

I know how to use the member initializer list to specify construction methods for individual objects. Can it also be used to initialize array elements?
No.
I am unware of the syntax if it can be.

There isn't any.

Victor

[Darius.Moos AT esigma-systems DOT de]

Thanks for the clarification.