2

I need to instantiate a free template function (FTF) within a template class (TC). The FTF takes as a template parameter one of the template parameters of the TC. The TC also holds generic pointers to these FTF's, and these functions are called through the pointers.

The step of taking a pointer to a FTF is not enough to instantiate it, and I receive linker errors from the GCC toolchain. MSDN illustrates FTF specification as so -- however my instantion of the FTF is dependant on a template parameter of my TC, and therefore the FTF instantiation cannot be placed in free scope.

Is this possible ? I am attaching some basic generated code, the issue is in the constructor of the class test_service, where I assign the pointer of a free function into a custom container. I get a linker error telling me the free function cannot be found (uninstantiated). I know that specifying a call to the template function in the class somewhere will produce a instantiation, however I am only going to be making a call via a pointer.

#include "rpc_common.h"
#include <boost/cstdint.hpp>

namespace rubble { namespace rpc {

  struct test_service_dummy_tag{};

  template<typename T>
  class test_service_skel
  {
  public:
    bool Init() {}
    bool TearDown() {}
    bool test_one(TestRequest,TestResponse){};
  private:
  };

  template<typename T_IMPL>
  bool test_service_test_one(T_IMPL & impl,ClientRequest & request)
  {
    return 0;
  }

  template<typename T_IMPL=test_service_skel<test_service_dummy_tag> >
  class test_service
  {
  public:
    test_service()
    {
      // uncomment the following two lines and a instantiation will occur.
      // ClientRequest cr;
      //test_service_test_one<T_IMPL>(m_impl,cr);
      m_dispatch_table.SetEntry( Oid("test_one",0),(void *)  & test_service_test_one<T_IMPL>);
    }
    bool Init() { return m_impl.Init(); };
    bool TearDown() { return m_impl.TearDown(); };
  private:
    T_IMPL m_impl;
    OidContainer<Oid,void *> m_dispatch_table;
  };


} }

EDIT: self-contained minimal version

 class test_skel
    {
      bool test_function()
      {
        return true;
      }
    };


    template<typename T>
    bool test_function()
    {

    }

    template<typename T = test_skel>
    class test
    {
    public:
      test()
      {
        dispatch = (void *) & test_function<T>;
      }
      void * dispatch;
    };

    int main()
    {
      test<> t;
      return 0;
    }
4

2 回答 2

2

如果您不使用 a 没有问题void*，即：http ://www.ideone.com/eRgUG

但是，如果您坚持将指针存储在 a 中void*，那么您需要先使用特定的函数指针获取地址，然后再进行转换 - 例如

    bool (*temp)() = &test_function<T>;
    dispatch = reinterpret_cast<void*>(temp); // YUCK

这为编译器提供了足够的上下文来为您生成地址。

啊 - 刚刚看到 DeadMG 的答案，生成的功能void*更整洁......

于 2011-07-07T11:52:50.727 回答
1

当没有重载时，使用 MSVC 时，您的自包含示例不会为我编译一个关于重载函数的奇怪错误。但是，我确实设法解决了它。

class test_skel
{
    bool test_function()
    {
        return true;
    }
};

template<typename T> void* to_void_pointer(T t) {
    return reinterpret_cast<void*>(t);
}

template<typename T>
bool test_function()
{
    return true;
}

template<typename T = test_skel>
class test
{
public:
    test()
    {
        dispatch = to_void_pointer(&test_function<T>);
    }
    void * dispatch;
};

int main()
{
    test<> t;
    return 0;
}

这编译得很干净。我怀疑你看到的和我看到的任何行为都是编译器错误。

于 2011-07-07T11:52:56.367 回答