C++ Primer 5th Edition Exercises(練習題)13.28

c++ c/c++系列文章 c++ primer 5th e exercise

孫守真任真甫 2020-04-01 04:27:57 ‧ 1287 瀏覽

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Exercise 13.28: Given the following classes, implement a default constructor and the necessary copy-control members.

(a)
class TreeNode {
private:
std::string value;
int count;
TreeNode *left;
TreeNode *right;
};
(b)
class BinStrTree {
private:
TreeNode *root;
};

如下類別，請試著實作出它們的預設建構器（default constructor）和必要的拷貝控制成員。

TreeNode.h

#ifndef TREENODE_H
#define TREENODE_H
#include<string>
class TreeNode
{
public:
    TreeNode() : count(0), left(nullptr), right(nullptr), user_cntr(new size_t(1)) {};//預設建構器（default constructor）
    TreeNode(const std::string& s) :value(s),
        count(s.size()), left(new TreeNode[s.size()]), right(left + s.size() - 1), user_cntr(new size_t(1)) {}//預設建構器
    //拷貝建構器
    TreeNode(const TreeNode& tn) :
        value(tn.value), count(tn.count), left(tn.left), right(tn.right),user_cntr(tn.user_cntr) {
        ++* user_cntr;
    }
    ~TreeNode() {
        if (-- * user_cntr == 0) {
            delete[]left;
            //left = nullptr; right = nullptr;
            delete user_cntr;
        }
    }
    TreeNode& operator=(const TreeNode& rhs) {
        ++* rhs.user_cntr;
        if (--*user_cntr==0)
        {
            delete[]left;
            //left = nullptr; right = nullptr;
            delete user_cntr;
        }
        value = rhs.value;
        count = rhs.count;
        left = rhs.left;
        right = rhs.right;
        user_cntr = rhs.user_cntr;
        return *this;
    }
private:
    std::string value;
    int count;
    TreeNode* left;//由此想到動態陣列（動態配置多個物件）；再由new[]想到要解構delete[]
    TreeNode* right;
    size_t* user_cntr;
};

#endif // !TREENODE_H

BinStrTree.h

#ifndef BINSTRTREE_H
#define BINSTRTREE
#include"TreeNode.h"
class BinStrTree
{
public:
    //BinStrTree():root(nullptr){}//預設建構器
    BinStrTree(const std::string& s=std::string()):root(new TreeNode(s)),user_cntr(new size_t(1)){}
    BinStrTree(TreeNode* tnp):root(tnp),user_cntr(new size_t(1)){}
    //拷貝建構器
    BinStrTree(const BinStrTree& bst) :root(bst.root), user_cntr(bst.user_cntr){++* user_cntr;}
    //拷貝指定運算子
    BinStrTree& operator=(const BinStrTree & bst ){
        ++*bst.user_cntr;
        if (--*user_cntr==0)
        {
            delete root;
            delete user_cntr;
        }
        root = bst.root;
        user_cntr = bst.user_cntr;
        return *this;
    }
    //解構器
    ~BinStrTree() {
        if (-- * user_cntr == 0) {
            delete root;
            delete user_cntr;
        }
    }
private:
    TreeNode* root;
    size_t* user_cntr;
};


#endif // !BINSTRTREE_H

.cpp

#include<string>
#include"TreeNode.h"
#include"BinStrTree.h"
using namespace std;
int main() {
    TreeNode tn,tn1("孫守真"),tn2(string("阿彌陀佛"));
    tn = tn1;
    TreeNode tn3(tn2);
    tn = tn2;
    tn1 = tn3;
    BinStrTree bst("妙音如來"),bst1(bst),bst2,bstp(new TreeNode(tn3));
    bst2 = bst;
    bstp = bst2;
}

https://github.com/oscarsun72/prog1-C-Primer-5th-Edition-s-Exercises/tree/exercise13_28a/prog1

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13.2 拷貝控制與資源管理 13.2.2. Defining Classes That Act Like Pointers Defining a Reference-Counted Class~ 練習13.28
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