From: Martin Wille (mw8329_at_[hidden])
Date: 2004-07-01 00:36:19
Eric Niebler wrote:
> Martin Wille wrote:
...
>> #include <boost/minmax.hpp>
>>
>> int foo()
>> {
>> BOOST_USING_STD_MIN();
>> return min BOOST_PREVENT_MACRO_SUBSTITUTION(3, 4);
>> }
>>
>> namespace notboost
>> {
>> template <typename T>
>> T const &
>> proxy_min(T const &p, T const &q)
>> {
>> BOOST_USING_STD_MIN();
>> return min BOOST_PREVENT_MACRO_SUBSTITUTION(p, q); // line 16
>> }
>> }
>>
>> int bar()
>> {
>> return notboost::proxy_min(3, 4); // line 22
>> }
>>
>>
>> namespace test
>> {
>> int baz()
>> {
>> BOOST_USING_STD_MIN();
>> return min BOOST_PREVENT_MACRO_SUBSTITUTION(3, 4);
>> }
>> }
>>
>> int main() { foo(); bar(); test::baz(); }
>>
>>
>> The compiler emits these error messages:
>> min.cpp: In function `const int & notboost::proxy_min<int>(const int
>> &, const int &)':
>> min.cpp:22: instantiated from here
>> min.cpp:16: `min' undeclared (first use this function)
>> min.cpp:16: (Each undeclared identifier is reported only once
>> min.cpp:16: for each function it appears in.)
>
> Ugh. Thanks Martyn. Can you tell me if there is something funny about
> the way STLPort defines std::min/max? Does it use macros? Or are they
> defined globally and imported into the std:: namespace with using
> declarations?
STLPort implements std::min in the namespace _STL.
BOOST_USING_STD_MIN() correctly expands to: using _STL ::min
The (shortened) result of preprocessing is:
namespace _STL {
template <class _Tp>
inline const _Tp& (min)(const _Tp& __a, const _Tp& __b) { return __b <
__a ? __b : __a; }
template <class _Tp>
inline const _Tp& (max)(const _Tp& __a, const _Tp& __b) { return __a <
__b ? __b : __a; }
template <class _Tp, class _Compare>
inline const _Tp& (min)(const _Tp& __a, const _Tp& __b, _Compare __comp) {
return __comp(__b, __a) ? __b : __a;
}
template <class _Tp, class _Compare>
inline const _Tp& (max)(const _Tp& __a, const _Tp& __b, _Compare __comp) {
return __comp(__a, __b) ? __b : __a;
}
}
(the complete preprocessed source can be found at:
http://tinyurl.com/yrflf )
I must be blind, I can't spot the line that hoists the contents of
_STL:: into std::.
> In the worst case, I suppose for this compiler/library combination we
> can import std::min/max into the boost namespace with a using
> declaration and make BOOST_USING_STD_MIN() expand to nothing. Martyn,
> can you try that and see if it works?
Changing the source to
namespace notboost
{
BOOST_USING_STD_MIN(); // moved to namespace scope
template <typename T>
T const &
proxy_min(T const &p, T const &q)
{
return min BOOST_PREVENT_MACRO_SUBSTITUTION(p, q);
}
}
indeed makes gcc-2.95.3 accept the code.
Regards,
m