Re: Xcode-users Digest, Vol 10, Issue 29
Re: Xcode-users Digest, Vol 10, Issue 29
- Subject: Re: Xcode-users Digest, Vol 10, Issue 29
- From: Aaron Montgomery <email@hidden>
- Date: Sat, 26 Jan 2013 11:18:41 -0800
I think you are misreading the original code (as I think Chris did last night), this isn't an issue with typedef-ing a pointer. The original poster actually just typedef-ing an int:
Original Poster: typedef char char_T;
What Seems to be Your Interpretation: typedef char* char_T;
The following:
typedef char char_T;
int f(int argc, const char* argv[])
int f(int argc, const char_T* argv[])
{
return 0;
}
compiles without complaint, and
typedef char char_T;
int main(int argc, const char* argv[])
{
return 0;
}
also compiles without complaint, and
typedef char char_T;
int main(int argc, char_T* argv[])
{
return 0;
}
also compiles without complaint, but
typedef char char_T;
int main(int argc, const char_T* argv[])
{
return 0;
}
raises the error that argv should be of type char**.
So clang seems to expect that either main is called with a second argument of const char** or main is called with a second argument of T** where T is a typedef of char, but main cannot be called with a second argument of const T** where T is a typedef of char. However, this inconsistency is not seen with functions which can be declared with prototypes using "const char**" and implemented with definitions using "const char_T**"
Aaron
On Jan 26, 2013, at 10:55 AM, Feliks Kluzniak <email@hidden> wrote:
> This is a well-known feature of C, apparently inherited by C++. I quote from Harbison and Steele, C - A Reference Manual, FifthEdition, p. 90:
>
> "typedef int *int_pointer;
> const int_pointer const_pointer;
>
> This makes const_pointer look like a "pointer to constant int_pointer", but it is not -- it is still a constant pointer to a (nonconstant) int."
>
> Then they point out that this may be rewritten as
>
> int_pointer const const_pointer;
>
> If you substitute the type definition you see
>
> int * const const_pointer;
>
> and light dawns. :-)
>
> Personally, I find that it helps me to avoid the confusion if I always write "const" after the type to which it refers, i.e.,
>
> int const * p;
> int * const p;
>
> etc.
>
> -- Feliks
>
>
> On Jan 26, 2013, at 16:47, email@hidden wrote:
>
>> Date: Fri, 25 Jan 2013 20:54:02 -0800
>> From: Aaron Montgomery <email@hidden>
>> To: Dmitry Markman <email@hidden>
>> Cc: "email@hidden list" <email@hidden>
>> Subject: Re: clang can not compile simple cpp file with main's second
>> argument is typedef
>> Message-ID: <email@hidden>
>> Content-Type: text/plain; charset=us-ascii
>>
>>
>> On Jan 25, 2013, at 7:37 PM, Dmitry Markman <email@hidden> wrote:
>>
>>> #include <iostream>
>>>
>>> typedef char char_T;
>>>
>>> int main(int argc, const char_T * argv[])
>>> {
>>> std::cout << "Hello Test World!" << std::endl;
>>> return 0;
>>> }
>>
>> If you eliminate the const, and pass a char_T** it compiles (and I think the standard char** not a const char**). What is odd to me is that it will compile if you pass a const char**, but not a const char_T**.
>>
>> Aaron
>
>
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