C ++模板类继承

幻想_RQG

如何定义从模板类继承的模板类？

我想包装std::queue并std::priority_queue进入基类。以我为例LooperQueue。我用StdQueue这种方式auto queue = new StdQueue<LooperMessage *>()。

我的班级定义编译器抱怨

错误日志：

  In file included from /Users/rqg/ASProjects/PboTest/muses/src/main/cpp/Painter.cpp:10:
  /Users/rqg/ASProjects/PboTest/muses/src/main/cpp/util/StdQueue.h:14:5: error: unknown type name 'size_type'; did you mean 'size_t'?
      size_type size() override;
      ^~~~~~~~~
      size_t
  /Users/rqg/Library/Android/sdk/ndk-bundle/toolchains/llvm/prebuilt/darwin-x86_64/lib64/clang/5.0.300080/include/stddef.h:62:23: note: 'size_t' declared here
  typedef __SIZE_TYPE__ size_t;
                        ^
  In file included from /Users/rqg/ASProjects/PboTest/muses/src/main/cpp/Painter.cpp:10:
  /Users/rqg/ASProjects/PboTest/muses/src/main/cpp/util/StdQueue.h:16:5: error: unknown type name 'reference'
      reference front() override;
      ^
  /Users/rqg/ASProjects/PboTest/muses/src/main/cpp/util/StdQueue.h:20:21: error: unknown type name 'value_type'; did you mean 'ARect::value_type'?
      void push(const value_type &x) override;
                      ^~~~~~~~~~
                      ARect::value_type
  /Users/rqg/Library/Android/sdk/ndk-bundle/sysroot/usr/include/android/rect.h:44:21: note: 'ARect::value_type' declared here
      typedef int32_t value_type;

码：

#ifndef PBOTEST_LOOPERQUEUE_H
#define PBOTEST_LOOPERQUEUE_H

#include <queue>
#include <cstdlib>

template<typename Tp, typename Sequence = std::deque<Tp> >
class LooperQueue {
public:

    typedef typename Sequence::value_type                value_type;
    typedef typename Sequence::reference                 reference;
    typedef typename Sequence::const_reference           const_reference;
    typedef typename Sequence::size_type                 size_type;
    typedef          Sequence                            container_type;


    virtual size_type size()  = 0;

    virtual reference front() = 0;

    virtual void pop()= 0;

    virtual void push(const value_type &x) = 0;
};


#endif //PBOTEST_LOOPERQUEUE_H

 #ifndef PBOTEST_STDQUEUE_H
#define PBOTEST_STDQUEUE_H


#include "LooperQueue.h"

template<typename Tp, typename Sequence = std::deque<Tp> >
class StdQueue : public LooperQueue<Tp, Sequence> {
public:
    size_type size() override;

    reference front() override;

    void pop() override;

    void push(const value_type &x) override;

public:


private:
    std::queue<Tp, Sequence> mQueue;
};


#endif //PBOTEST_STDQUEUE_H

songyuanyao

这里的问题是，基类LooperQueue是一个依赖的基类，它依赖于template参数Tp和Sequence，然后在不知道模板参数的情况下就无法确定其完整类型。标准C ++说，非依赖的名字（例如size_type，reference和value_type）将不会在依赖基类中查找。

要更正代码，只需使名称受基类名称的限制即可；那么只能在实例化时查找这些名称，届时将知道必须探索的确切基础专业知识。例如

template<typename _Tp, typename _Sequence = std::deque<_Tp> >
class StdQueue : public LooperQueue<_Tp, _Sequence> {
public:
    typename LooperQueue<_Tp, _Sequence>::::size_type size() override;
    typename LooperQueue<_Tp, _Sequence>::reference front() override;
    void pop() override;
    void push(const typename LooperQueue<_Tp, _Sequence>::value_type &__x) override;
private:
    std::queue<_Tp, _Sequence> mQueue;
};

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