Re: A question on variable defination



Eric Sosman wrote On 03/31/06 14:08,:

[... a bunch of nonsense he regrets ...]

sunnylele wrote On 03/31/06 13:11,:

Hi, all,

a question on the following defination:
an external function is defined as:
nmriopen(char *const filename, const int np1, const float step1,
const int np2, const float step2)

what's the difference if it is defined as:
nmriopen(char filename, int np1, float step1,
int np2, float step2)


I assume you mean `char *filename' rather than
`char filename'.

[...]
For the pointer argument things are a little different,
because the thing that is `const' isn't the pointer value
itself, but the thing it points at. (In this case; it's
possible to get the other effect instead, or in addition.)

Ahh, blagnabbit! I mis-read your declaration, and made
a fool of myself. `char * const filename' is a pointer to
`char', where the pointed-to `char' is modifiable but the
pointer variable itself is not. As with the other `const'-
qualified arguments, this is not terribly useful. (Hence
seldom used, hence unfamiliar, hence easily mis-read by
overconfident shoot-from-the-hip people ...)

and what if use "int *const np1" instead of "const int np1"?

A similar effect: The function promises (weakly) not to
use the pointer `np1' to change the value that it points at.

Same mistake by yours truly: The pointer variable `np1'
is unchangeable, but the integer that it points to can be
modified.

--
Eric.Sosman@xxxxxxx

.

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