Hi.
You know, this question is off-topic on the MySQL list.
On Wed, Feb 14, 2001 at 09:54:44AM +0000, [EMAIL PROTECTED] wrote:
> Hi folks,
>
> I am trying to compile a simple program to play with mysql. But i am
> running into single problems, but i guess easy to solve by too many of
> the wizards here.
>
> I am too paranoic when compiling my programs, so i activate all warnning
> (at least i try) flags to gnu c compiler.
>
> The problem occurs when type conversion: type conversion is automatic
> when a functions takes a single pointer to const anything, but when
> there is a double pointer to a const type and i pass double pointer to a
> non const type i run into problem? Why in the later case conversion is
> not automatic? the former is.
This is a FAQ, see e.g. http://faqs.jmas.co.jp/FAQs/C-faq/faq, section
11.10. For a somewhat better explanation have a look at the C++ FAQ
(and also applies to your C program):
http://reality.sgi.com/austern_mti/std-c++/faq.html#C1
The summary is that one could bypass the const qualifier c() adds (not
in your example, but in general).
> Here is the simple code (just to test):
>
> #include <stdio.h>
>
> int
> t(const int *i)
> {
> printf("%d\n", *i);
> return 0;
> }
>
> void
> c(const char **reg)
With C++, you can declare it as
void c(const char * const* reg)
but this does not seem to be allowed in C (I am not used to C anymore,
but gcc 2.95.3 complains).
> {
> while (*reg)
> printf("%s\n", *reg++);
> }
>
> int
> main(int argc, char *argv[])
> {
> int i;
> char *reg[] = {
> "Gustavo",
> "Vieira",
> "Goncalves",
> "Coelho", "Rios", NULL};
The other way is to declare "reg" to what is really is, instead:
const char *reg[] = ...
This will also work with C.
The solution of the C-FAQ is dirty (as it opens the hole again because
of which the auto cast is not made) and should IMHO be avoided, if
possible.
Bye,
Benjamin.
> i = 10;
>
> (void) t(&i);
> c(reg);
>
> return 0;
> }
>
>
> But when compiling:
>
> grios@etosha$ cc -ansi -pedantic -Wconversion -Wall -Werror t.c
> cc1: warnings being treated as errors
> t.c: In function `main':
> t.c:30: warning: passing arg 1 of `c' from incompatible pointer type
> grios@etosha$
[...]
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