C++Talk.NET

Tomás · Guest

I'm sure a lot of you have seen the following code which demonstrates why
we can't implicitly convert from:-

char**

to:

const char**

Here's the code (written originally by James Kanze):

const char c = 'a';
char* p;
char** pp = &p;
const char** ppc = pp; // Supposing that this were not illegal.

*ppc = &c; // Oops: where does p point?
*p = 'b'; // And what is wrong here?

I've read the above code many times but never understood it. Even when I
thought about it thoroughly and slowly, I couldn't comprehend what was
going on.

Anyway, I came across the code again today, and finally I resolved to
grasp an understanding of it once and for all. So I drew a diagram, which,
after a few minutes of analysing, made me understand. With the hope of
helping others, here's the diagram:

http://img315.imageshack.us/img315/2876/undconst6kk.jpg

I've posted this to more than one newsgroup, so if you would like to
reply, I'd appreciate if you would keep the discussion in comp.lang.c++.

-Tomás

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