Re: [AD] The details of 'const'

[Laurence Withers <lwithers@xxxxxxxxxx>]

In reply to Ben Davis <ben@xxxxxxxxxx>:
>Hence, at least in DJGPP, it *is* possible to tell the compiler exactly 
>what we mean. In this case, we want a pointer to a variable pointer to a 
>constant string, so "const char **" is fine for ugetx(). It just means 
>that the string is constant; not the pointer.

This isn't the same; that was why I introduced ugetxc() in the first
place. Don't you get a warning/error when you try to compile the
following code?

int test(const char* p)
{
   return ugetx(&p);
}

The *reason* is this: if you pass a ptr-to-ptr-to-char to a function
expecting a ptr-to-ptr-to-const-char, then that function *might* set the
ptr-to-ptr to point at some const char data. Then, when the function
returns, the code executed after the function doesn't see that char data
as const-qualified. Hence the error.

Also, you can look in the C FAQ-list, which tells you that the process
by which non-const data can be passed to a const-function only goes down
one level, although it doesn't explain why.

Bye for now,
-- 
Laurence Withers, lwithers@xxxxxxxxxx
                http://www.lwithers.demon.co.uk/

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