From: Nick <jp_prongs AT yahoo DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Vector of Classes issue in GCC 3.1
Date: Wed, 12 Jun 2002 13:13:07 -0400
Organization: MindSpring Enterprises
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Let's say you have a class like:

class foo {
	char *a;
	foo() { a = malloc(100); }
	~foo() { free(a); }
};

Then doing this:

foo *bar = new foo;
foo *baz = new foo(bar);
delete bar;

will cause baz.a to point to a free()d memory block, messing up your program. This is because, by
default, baz.a will be the same as bar.a. To fix that, you can use this class:

class foo2 {
	char *a;
	foo() { a = malloc(100); }
	foo(foo& orig) { a = malloc(100); memcpy(a, orig.a, 100); }
	foo& operator=(foo& orig) { memcpy(a, orig.a, 100); }
	~foo() { free(a); }
};

The foo(foo& orig), the copy constructor, allocates a new block and copies the original object's
block to it. The operator= causes statements like "foo baz = bar;" to work OK, by copying the data
pointed to by bar.a to baz.a.