On 13/10/2017 07:16, Gregory Ewing wrote:
Steve D'Aprano wrote:
On Fri, 13 Oct 2017 03:37 pm, Gregory Ewing wrote:
If the compiler can tell where p is initially pointing, it could
put the pointer in read-only memory.
If it's read-only, how can the compiler write to it?
(I come from the days when ROM was actual ROM, burned in at the factory.)
So, the factory is allowed to write to it. Possibly
it's writing data that came from... a compiler?
A memory that couldn't be written to at all, ever, would
be a bit useless!
It's read-only in the same sense as a printed book; you can't change the
marks already on the page.
I've programmed EPROMS. Neither the C language nor the concept of
'const' attributes for data ever came into it. While executable code
doesn't really need it.
It is simply not a necessity. You just arranged for writeable portions
of memory to be at different locations than that containing the code and
fixed data. Sometimes it was only data.
'const' is anyway the wrong sort of attribute to use, as I've already
explained. For example:
const int A = rand(); // inside a function
A is written to multiple times at runtime. It can't go into actual
read-only memory like a ROM. And it might have trouble going into a
memory page with read-only attributes.
'const' tries to do too many things, most of them poorly, although it
does a very good job at adding clutter.
--
bartc
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