Question

我必须创建一个双链表列表，它继承自DoubleListInterface.h

我正在编译，但我遇到了错误：

rascal>parse(#start[Program], readFile(|project://rascal-test-library/src/hello.pico|), |project://rascal-test-library/src/hello.pico|)
start[Program]: (start[Program]) `begin declare input : natural,  
              output : natural,           
              repnr : natural,
              rep : natural;
      input := 14;
      output := 1;
      while input - 1 do        
          rep := output;
          repnr := input;
          while repnr - 1 do
             output := output + rep;
             repnr := repnr - 1
          od;
          input := input - 1
      od
end`

从我在这里的另一个线程中读取的内容，＆＃34;您需要使用与基类完全相同的参数类型来定义函数。＆＃34;

我不知道为什么，但那只是没有点击我的脑袋。

project3.cpp：

project3.cpp:19:21: error: cannot declare variable "list" to be of abstract type 'DoubleList<int>'
   DoubleList<int> list;
                   ^

DoubleList.h：

#include <iostream>
#include <stdlib.h>
#include "DoubleList.cpp"

int failures = 0;

void test(int result, int expected) {
    if (result != expected) {
        std::cout << "test FAILED: expected(" << expected << ") but result(" << result << ")" << std::endl;
        failures++;
    }
}

int main(int argc, char **argv) {
    DoubleList<int> list;

    test(list.isEmpty(), true);
    test(list.getLength(), 0);

    list.insertFront(5);
    list.insertFront(7);
    list.insertBack(8);
    list.insertFront(2);

    test(list.isEmpty(), false);
    test(list.getLength(), 4);
    test(list.getEntry(1), 2);
    test(list.getEntry(2), 7);
    test(list.getEntry(3), 5);
    test(list.getEntry(4), 8);

    list.remove(1);
    test(list.getLength(), 3);
    test(list.getEntry(1), 7);
    test(list.getEntry(2), 5);
    test(list.getEntry(3), 8);

    list.remove(3);
    test(list.getLength(), 2);
    test(list.getEntry(1), 7);
    test(list.getEntry(2), 5);

    list.clear();
    test(list.isEmpty(), true);
    test(list.getLength(), 0);

    if (failures == 0)
        std::cout << "ALL TESTS PASSED" << std::endl;
    else
        std::cout << failures << " TESTS FAILED" << std::endl;

    return 0;
}

DoubleList.cpp（到目前为止）：

#ifndef DOUBLE_LIST_
#define DOUBLE_LIST_

#include "DoubleListInterface.h"
#include "DoubleNode.cpp"

template<class ItemType>
class DoubleList : public DoubleListInterface<ItemType>
{
private:
    ItemType item;
    DoubleList<ItemType>* head;
    DoubleList<ItemType>* tail;

protected:
    // PUT DOUBLELIST METHODS HERE

public:
    // PUT INTERFACE METHODS HERE

    //DoubleList(const ItemType& anItem, DoubleList<ItemType>* headPtr, DoubleList<ItemType>* tailPtr);
    //~DoubleList(); <---------- Not sure if I need these or if I even implemented them right, so they're commented out for now

    bool isEmpty() const;
    int getLength() const;
    bool insertFront(const ItemType& newEntry);
    bool insertBack(const ItemType& newEntry);
    bool remove(int position);
    void clear();
    ItemType getEntry(int position);
};

#endif

DoubleListInterface.h：

#include "DoubleListInterface.h"
#include "DoubleList.h"
#include <iostream>

int itemCount = 0;

template<class ItemType>
bool DoubleList<ItemType>::isEmpty() const
{
    if (this->head == nullptr)
        return true;
    else
        return false;
}

template<class ItemType>
int DoubleList<ItemType>::getLength() const
{
    return 0;
}

template<class ItemType>
bool DoubleList<ItemType>::insertFront(const ItemType& newEntry)
{
    return true;
}

很抱歉，如果它很多，我现在真的迷失了。

Answer 1

ItemType getEntry(int position);不会覆盖相应的DoubleListInterface方法。请注意缺少const限定符。您应该使用override说明符来避免此类问题

// Would trigger compilation error when base class
// does not have a virtual method with this exact signature.
ItemType getEntry(int position) override;

不能将变量声明为抽象类型

1 个答案: