Changes between Version 10 and Version 11 of const

Timestamp:

Oct 30, 2013, 12:48:19 AM (10 years ago)

Author:

andersk@mit.edu

Comment:

Make it clearer why foo ** → const foo ** would be bad

const

@@ -16 +16 @@
 `foo *` may be implicitly converted to `const foo *`, but not the other way around.
 
-`foo **` may be implicitly converted to `foo *const *` (as a special case of the above), but may ''not'' be converted to `const foo **` (otherwise, you could write through `const foo *p` as follows: `foo *q; const foo **pq = &q; *pq = p; *q = …;`).
+`foo **` may be implicitly converted to `foo *const *` (as a special case of the above), but may ''not'' be converted to `const foo **` (otherwise, you would not be protected from writing to `const foo f`, as follows: `foo *p; const foo **pp = &p; *pp = &f; *p = …;`).
 
 However, it is safe to convert `foo **` to `const foo *const *`.  C++ lets you do this implicitly (conv.qual 4 in the standard); for no particular reason, C does not.