Question

#include <iostream>
#include <vector>
#include <string>
#include <ostream>
#include <algorithm>

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/cast.hpp>

using namespace std;

class tape_recorder {
public:
  void play() {
    std::cout << "Since my baby left me...\n";
  }

};

template <typename R, typename Arg> 
class invoker_base {
public:
  virtual R operator()(Arg arg)=0;
};
template <> 
class<void, void> invoker_base {
public:
  virtual void operator()(void)=0;
};


template <typename R, typename Arg, typename T> 
class member_ptr_invoker : public invoker_base<R,Arg> {
  R (T::*func_)(Arg);
  T* t_;
public:
  member_ptr_invoker(R (T::*func)(Arg),T* t)
    :func_(func),t_(t) {}

  R operator()(Arg arg) {
    return (t_->*func_)(arg);
  }
};
template <typename T> 
class member_ptr_invoker<void, void, T> : public invoker_base<void,void> {
  void (T::*func_)(void);
  T* t_;
public:
  member_ptr_invoker(void (T::*func)(void),T* t)
    :func_(func),t_(t) {}

  void operator()(void arg) {
    return (t_->*func_)(arg);
  }
};

int main(void)
{
  tape_recorder tr;

  // member_ptr_invoker
  member_ptr_invoker<void, void, tape_recorder> mpi(&tape_recorder::play, &tr);
  //mpi();

  return 0;
}

编译器错误：

g++ -o p337 p337.cpp -Wall
p337.cpp:47:6: error: expected identifier before ‘<’ token
p337.cpp:47:6: error: expected unqualified-id before ‘<’ token
p337.cpp: In instantiation of ‘invoker_base<void, void>’:
p337.cpp:66:74:   instantiated from here
p337.cpp:44:13: error: invalid parameter type ‘void’
p337.cpp:44:13: error: in declaration ‘virtual R invoker_base<R, Arg>::operator()(Arg)’
p337.cpp:73:24: error: ‘arg’ has incomplete type
p337.cpp:73:27: error: invalid use of ‘void’

问题＆GT;如何修复编译错误？

谢谢

// ============ Fixed version =======================
#include <iostream>
#include <vector>
#include <string>
#include <ostream>
#include <algorithm>

#include <boost/function.hpp>
#include <boost/bind.hpp>
#include <boost/cast.hpp>

using namespace std;

class tape_recorder {
public:
  void play() {
    std::cout << "Since my baby left me...\n";
  }

  void stop() {
    std::cout << "OK, taking a break\n";
  }

  void forward() {
    std::cout << "whizzz\n";
  }

  void rewind() {
    std::cout << "zzzihw\n";
  }

  void record(const std::string& sound) {
    std::cout << "Recorded: " << sound << '\n';
  }
};

int roundToInt(double d)
{
  return boost::numeric_cast<int> (d + 0.5);
}

template <typename R, typename Arg> 
class invoker_base {
public:
  virtual R operator()(Arg arg)=0;
};
template <> 
class invoker_base<void, void> {
public:
  virtual void operator()(void)=0;
};

template <typename R, typename Arg, typename T> 
class member_ptr_invoker : public invoker_base<R,Arg> {
  R (T::*func_)(Arg);
  T* t_;
public:
  member_ptr_invoker(R (T::*func)(Arg),T* t)
    :func_(func),t_(t) {}

  R operator()(Arg arg) {
    return (t_->*func_)(arg);
  }
};
template <typename T> 
class member_ptr_invoker<void, void, T> : public invoker_base<void,void> {
  void (T::*func_)(void);
  T* t_;
public:
  member_ptr_invoker(void (T::*func)(void),T* t)
    :func_(func),t_(t) {}

  void operator()() {
    return (t_->*func_)();
  }
};

int main(void)
{
  tape_recorder tr;

  // member_ptr_invoker
  member_ptr_invoker<void, void, tape_recorder> mpi(&tape_recorder::play, &tr);
  mpi();

  return 0;
}

Answer 1

这是您的模板专业化的问题。变化：

 class<void, void> invoker_base {

为：

 class invoker_base<void, void> {

错误：参数类型无效'void'

1 个答案: