Re: Strange "No matching function for call" compilation error with G++ 4.1

[Peter Doerfler <gcc at pdoerfler dot com>]

Yuanfei guo wrote:
> Hi there,
> 
> Just resend this letter again with adding reproduction code.  Any
> comments/suggestions are higly appreciated.
Now that really helps :)

> 
> I am porting some code to SUSE 10, with G++ 4.1. And hit an strange
> "no matching function call" compilation error.  I am confused because
> the calling function and candidate are nearly 100% same.
> 
> I wonder if this is a known G++ limitation or issue ? Because the same
> program got compiled with VC8.
> 
> Below is the compilation environment info and compilation error.
> 
> env info
> =========
> g++ (GCC) 4.1.0  (SLES10), can also be found with g++ 3.2 (UL1.0)
> 
> No compile option is added
> 
> 
> Compilation error
> =================
> no matching function for call to tdat_hash_map<MemAllocator<int>
>> ::func(MemAllocator<int>)
> 
> main.cpp:6: note: candidates are: static void
> tdat_hash_map<_AllocType>::func(_AllocType&)
> [with _AllocType = MemAllocator<int>]
> 
> 
> Repro code
> ===========
> template <class Type> class MemAllocator{};
> 
> template <class _AllocType> class tdat_hash_map {
> public:
>     typedef _AllocType _Alloc;
>     static void func(_Alloc&) {};
> };
> 
> int main()
> {
>     typedef tdat_hash_map<MemAllocator<int> > Map;
>     Map::func((MemAllocator<int>) (MemAllocator<int>()));
> 
>     return 0;
> }
> 
> 
> 
Replace main with:

int main()
{
    typedef tdat_hash_map<MemAllocator<int> > Map;
    MemAllocator<int> ma;
    Map::func(ma);

    return 0;
}

You were trying to get a reference to a temporary object by just calling
the constructor of MemAllocator where func expects a MemAllocator&.

The error message kind of contains this info as it says that it can't
find func(MemAllocator), note no reference.

A more intuitive error message would be nicer, I guess. E.g. icc9.1
tells you:
testKelvin.cpp(12): error: initial value of reference to non-const must
be an lvalue
      Map::func((MemAllocator<int>) (MemAllocator<int>()));

And Comeau (http://www.comeaucomputing.com/tryitout/) says the exact
same thing (hmm, is icc using the EDG front-end now?)

Note that even if VC8 decided to compile this code it most likely
wouldn't work properly. OTOH maybe you meant to pass a const ref anyway?

HTH, Peter

> 
> Thanks,
> -Kelvin
> 
> 
> On 9/27/06, Yuanfei guo <yuanfei8077@gmail.com> wrote:
>> Hi there,
>>
>> I am porting some code to SUSE 10, with G++ 4.1. And hit an strange
>> "no matching function call" compilation error.  I am confused because
>> the calling function and candidate are nearly 100% same.
>>
>> I wonder if this is a known G++ limitation or issue ? Because the same
>> program got compiled with VC8.
>>
>> Below is the compilation environment info and compilation error.
>>
>>  env info
>> =========
>> g++ (GCC) 4.1.0  (SUSE Linux)
>>
>> No compile option is added
>>
>>
>> Compilation error
>> ==============
>>  ./Cache/CacheManager.h:424: error: no matching function for call to
>> tdat_hash_map<std::basic_string<wchar_t, std::char_traits<wchar_t>,
>> std::allocator<wchar_t> >, Element<unsigned int, SqlObjectDefn,
>> std::basic_string<wchar_t, std::char_traits<wchar_t>,
>> std::allocator<wchar_t> > >*,
>> MemAllocator<std::pair<std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> >, Element<unsigned
>> int, SqlObjectDefn, std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> > >*> >
>> >::tdat_hash_map1(MemAllocator<std::pair<std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> >, Element<unsigned
>> int, SqlObjectDefn, std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> > >*> >, int)
>>
>> ./Common/TdatHashMap.h:250: note: candidates are: static void
>> tdat_hash_map<_Key, _Tp, _AllocType>::tdat_hash_map1(_AllocType&, int)
>> [with _Key = std::basic_string<wchar_t, std::char_traits<wchar_t>,
>> std::allocator<wchar_t> >, _Tp = Element<unsigned int, SqlObjectDefn,
>> std::basic_string<wchar_t, std::char_traits<wchar_t>,
>> std::allocator<wchar_t> > >*, _AllocType =
>> MemAllocator<std::pair<std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> >, Element<unsigned
>> int, SqlObjectDefn, std::basic_string<wchar_t,
>> std::char_traits<wchar_t>, std::allocator<wchar_t> > >*> >]
>>
>>
>>
>> Any comments/suggestions are higly appreciated.
>>
>> Thanks,
>> -Kelvin
>>