> On Dec 2, 2015, at 12:00 PM, Jonathan Prescott <[email protected]> wrote:
>
> In C++, “this” is a read-only (const) pointer setup during construction of
> the instance. Once an instance of a class is successfully created, the
> “this” pointer is guaranteed to be non-null for the lifetime of the instance.
>
No. It’s not a _part of_ the instance, it’s a _pointer to_ the instance. It
only exists as an invisible parameter passed to a method.
For example, the method foo::method(int x) is internally implemented as a
function [with a mangled name] that takes a parameter list (foo *this, int x).
And calling f->method(1) is exactly like calling that function with parameter
list (f, 1). Assuming the method is non-virtual. If it’s virtual, this gets
more complicated.
> I tried out a couple of ways of trying to modify the “this" pointer of an
> existing class instance, and the clang and gcc compilers would not allow that
> operation to compile.
Again, ‘this’ doesn’t belong to the instance. It’s simply a function parameter.
Here’s a simple way to call a method with a NULL ‘this’:
struct foo {
void method() {
printf(“this = %p\n”, this);
}
}
foo *f = NULL;
f->method();
—Jens _______________________________________________
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