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Date: Fri, 18 Feb 2011 17:36:00 -0000
From: Marc Glisse <marc.glisse@inria.fr>
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To: gcc-help <gcc-help@gcc.gnu.org>
cc: zhang qingshan <steven.zhang54373@gmail.com>
Subject: Re: why this testcase compile failed for gcc.
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On Fri, 18 Feb 2011, Ian Lance Taylor wrote:

> zhang qingshan <steven.zhang54373@gmail.com> writes:
>
>> /* ------- test case -------------------*/
>> void x();
>> template <typename T>
>> void foo(const T*);
>>
>> int main() {
>>    foo(x);
>> }
>>
>> GCC 4.5 complains:
>>
>> a.cpp: In function 'int main()':
>> a.cpp:6: error: no matching function for call to 'foo(void (&)())'
>>
>> It seems that, const T * is resolved as void (&)());
>>
>> IMO, T --> void (), const T --> void (), const T * --> void (*)(), and
>> it should be leagle.
>
> You are confusing function pointers with pointers to data objects.  They
> are not the same thing in C++.  That is, a function pointer is not a
> special type of pointer.

Well it still kind of is. Without the "const", the code compiles fine. But 
the fact that a const qualifier on a function type is ignored seems not to 
apply to template type deduction.

(note that most compilers behave like g++ here, except for clang which 
accepts the original code)

-- 
Marc Glisse