[英]C++ - Object of abstract class type is not allowed
目前正在研究由可調整大小的數組控制的堆棧的實現。 嘗試實例化ResizableArrayStack
的新對象會出錯。
E0322 object of abstract class type "csc232::ResizableArrayStack" is not allowed: ResizableArrayStack.cpp 107 function "csc232::ResizableArrayStack::isEmpty [with ItemType=int]" is a pure virtual function function "csc232::ResizableArrayStack::push [with ItemType=int]" is a pure virtual function function "csc232::ResizableArrayStack::pop [with ItemType=int]" is a pure virtual function function "csc232::ResizableArrayStack::peek [with ItemType=int]" is a pure virtual function
堆棧接口.h
#include "pch.h"
#pragma once
#ifndef CSC232_HW05_RESIZABLE_ARRAY_STACK_STACK_INTERFACE_H
#define CSC232_HW05_RESIZABLE_ARRAY_STACK_STACK_INTERFACE_H
namespace csc232 {
template<typename ItemType>
class StackInterface {
public:
/**
* Sees whether the stack is empty.
* @return True if the stack is empty, or false if not.
*/
virtual bool isEmpty() const = 0;
/**
* Adds a new entry to the top of this stack.
* @param newEntry The object to be added as a new entry.
* @return True if the addition is successful or false if not.
* @post If the operation was successful, newEntry is at the top of the stack.
*/
virtual bool push(const ItemType &newEntry) = 0;
/**
* Removes the top of this stack.
* @return True if the removal was successful or false if not.
* @post If the operation was successful, the top of the stack has been removed.
*/
virtual bool pop() = 0;
/**
* Returns a copy of the top of this stack.
* @return A copy of the top the stack.
* @post A copy of the top of the stack has been returned, and the stack is unchanged.
*/
virtual ItemType peek() const = 0;
/**
* Destroys this stack and frees its assigned memory
*/
virtual ~StackInterface() = default;
};
}
#endif //CSC232_HW05_RESIZABLE_ARRAY_STACK_STACK_INTERFACE_H
可調整大小的ArrayStack.h
#include "pch.h"
#pragma once
#ifndef CSC232_HW05_RESIZABLE_ARRAY_STACK_RESIZABLE_ARRAY_STACK_H
#define CSC232_HW05_RESIZABLE_ARRAY_STACK_RESIZABLE_ARRAY_STACK_H
#include "StackInterface.h"
namespace csc232 {
template <typename ItemType>
class ResizableArrayStack : public StackInterface<ItemType> {
private:
ItemType* items;
int top, capacity, count;
static const int DEFAULT_CAPACITY = 10;
public:
ResizableArrayStack();
ResizableArrayStack(int initial_capacity);
ResizableArrayStack(const ResizableArrayStack &rhs);
ResizableArrayStack(ResizableArrayStack &&rhs) = delete;
void operator=(const ResizableArrayStack<ItemType> &rhs);
void operator=(ResizableArrayStack &&rhs) = delete;
~ResizableArrayStack();
bool isEmpty() const = 0;
bool push(const ItemType &newEntry) = 0;
bool pop() = 0;
ItemType peek() const = 0;
int getCapacity() const;
private:
void init();
void increase_size();
};
#endif // CSC232_HW05_RESIZABLE_ARRAY_STACK_RESIZABLE_ARRAY_STACK_H
ResizableArrayStack.cpp
#include "pch.h"
#include <iostream>
#include "ResizableArrayStack.h"
template<typename ItemType>
csc232::ResizableArrayStack<ItemType>::ResizableArrayStack() : count(0), capacity(DEFAULT_CAPACITY) {
init();
}
template<typename ItemType>
csc232::ResizableArrayStack<ItemType>::ResizableArrayStack(int initial_capacity) : count(0), capacity(initial_capacity) {
init();
}
template<typename ItemType>
void csc232::ResizableArrayStack<ItemType>::init() {
items = new ItemType[capacity];
count = 0;
}
template<typename ItemType>
csc232::ResizableArrayStack<ItemType>::ResizableArrayStack(const ResizableArrayStack &rhs) {
*this = rhs;
}
template<typename ItemType>
void csc232::ResizableArrayStack<ItemType>::operator=(const ResizableArrayStack<ItemType> &rhs) {
if (this != rhs)
{
delete[] items;
init();
for (int i = 0; i < rhs.count; i++)
{
this->push(rhs.items[i]);
}
}
}
template<typename ItemType>
csc232::ResizableArrayStack<ItemType>::~ResizableArrayStack() {
delete[] items;
}
template<typename ItemType>
bool csc232::ResizableArrayStack<ItemType>::isEmpty() const {
return count == 0;
}
template<typename ItemType>
bool csc232::ResizableArrayStack<ItemType>::push(const ItemType &newEntry) {
if (count == capacity)
increase_size();
items[count] = newEntry;
return false;
}
template<typename ItemType>
bool csc232::ResizableArrayStack<ItemType>::pop() {
if (count == 0)
throw std::underflow_error("Underflow exception.");
count--;
return false;
}
template<typename ItemType>
ItemType csc232::ResizableArrayStack<ItemType>::peek() const {
top = capacity - 1;
return items[top];
}
template<typename ItemType>
int csc232::ResizableArrayStack<ItemType>::getCapacity() const {
return capacity;
}
template<typename ItemType>
void csc232::ResizableArrayStack<ItemType>::increase_size() {
capacity = capacity * 2;
ItemType *temp = new ItemType[capacity];
for (int i = 0; i < capacity; i++)
temp[i] = items[i];
delete[] items;
items = temp;
}
int main(int argc, char* argv[]) {
csc232::ResizableArrayStack<int> stack;
}
在您的ResizableArrayStack
類定義中,您的虛擬函數覆蓋仍然是“純”的:
bool isEmpty() const = 0;
bool push(const ItemType &newEntry) = 0;
bool pop() = 0;
ItemType peek() const = 0;
刪除= 0
並為了更好的衡量,告訴編譯器這些是覆蓋:
bool isEmpty() const override;
bool push(const ItemType &newEntry) override;
bool pop() override;
ItemType peek() const override;
如果任何虛函數的最終覆蓋是純虛的,則一個類是抽象的。 您對模板類ResizableArrayStack
定義具有= 0;
在幾個虛函數覆蓋的末尾。 這意味着它們被認為是純虛擬的,即使它們也有定義。 (定義純虛函數是有效的 C++,可以使用限定名稱調用定義,但仍必須由其他內容覆蓋以獲得非抽象類。)
只需從ResizableArrayStack
取出= 0
塊即可。
但還要注意,通常不應將帶有模板參數的定義放在 *.cpp 文件中:請參閱問答“為什么模板只能在頭文件中實現?”
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