复制构造函数, 深复制与浅复制

浅复制

#include<bits/stdc++.h>
using namespace std;

class StringTest
{
    private:
        char *str;
        int len;
        static int strings_count;
    public:
        StringTest(const char *s);//构造函数
        ~StringTest() ;
        void address();

        friend ostream & operator << (ostream & os, const StringTest & st);

};

// 设置strings_count 的初始值
int StringTest::strings_count=0; 

StringTest::StringTest(const char *s)
{
    len=strlen(s);
    str = new char[len+1];
    strcpy(str, s);
    strings_count++;
    cout<<"#"<<strings_count<<": \""<<str<<" \"对象已生成"<<endl;
}

StringTest::~StringTest()
{
    cout<<"\""<<str<<"\" object delete, ";
    strings_count--;
    cout<<strings_count<<" left"<<endl;
    delete [] str;
}

void StringTest::address()
{
    printf("%08X\n", str);
}

ostream & operator << (ostream & os, const StringTest & st)
{
    os<<st.str;
    return os;
}

int main()
{
    StringTest str1("Tabletennis");

    cout<<str1<<endl;

    StringTest str2 = str1;

    cout<<str2<<endl;

    //从结果可以看出两个字符串是指向的同一个位置, 这是默认的复制构造函数产生的结果 
    str1.address();
    str2.address();

    printf("%0X\n", &str1);
    printf("%0X\n", &str2);
    cout<<sizeof(StringTest)<<endl;

    return 0;
}

结果：

#1: "Tabletennis "对象已生成
Tabletennis
Tabletennis
001D68D0
001D68D0
6FFE00
6FFDF0
16
"Tabletennis" object delete, 0 left
"Tabletennis" object delete, -1 left

深复制

#include<bits/stdc++.h>
using namespace std;

class StringTest
{
    private:
        char *str;
        int len;
        static int strings_count;
    public:
        StringTest(const char *s);//构造函数
        StringTest(const StringTest & st);//复制构造函数
        StringTest() ;//默认构造函数 
        ~StringTest() ;
        void address();

        friend ostream & operator << (ostream & os, const StringTest & st);

};

// 设置strings_count 的初始值
int StringTest::strings_count=0; 

StringTest::StringTest(const char *s)
{
    len=strlen(s);
    str = new char[len+1];
    strcpy(str, s);
    strings_count++;
    cout<<"#"<<strings_count<<": \""<<str<<"\" 对象已生成 by 构造函数"<<endl;
}

StringTest::StringTest()
{
    len = 4;
    str = new char[30];
    strcpy(str, "Baseball");
    strings_count++;
    cout<<"#"<<strings_count<<": \""<<str<<"\" 对象已生成 by 默认构造函数"<<endl;
}

StringTest::StringTest(const StringTest & st)
{
    len = st.len;
    str = new char[len+1];
    strcpy(str, st.str);
    strings_count++;
    cout<<"#"<<strings_count<<": \""<<str<<"\" 对象已生成 by 复制构造函数"<<endl;
}

StringTest::~StringTest()
{
    cout<<"\""<<str<<"\" object delete, ";
    strings_count--;
    cout<<strings_count<<" left"<<endl;
    delete [] str;
}

void StringTest::address()
{
    printf("%08X\n", str);
}

ostream & operator << (ostream & os, const StringTest & st)
{
    os<<st.str;
    return os;
}

int main()
{
    StringTest str1("Tabletennis");

    cout<<str1<<endl;

    StringTest str2;

    cout<<str2<<endl;

    StringTest str3=str1;

    cout<<str3<<endl; 

    //从结果可以看出三个字符串的地址都不一样，这次是深拷贝 
    str1.address();
    str2.address();
    str3.address();

    printf("%0X\n", &str1);
    printf("%0X\n", &str2);
    printf("%0X\n", &str3);
    cout<<sizeof(StringTest)<<endl;

    return 0;
}

结果：

#1: "Tabletennis" 对象已生成 by 构造函数
Tabletennis
#2: "Baseball" 对象已生成 by 默认构造函数
Baseball
#3: "Tabletennis" 对象已生成 by 复制构造函数
Tabletennis
00B71510
00B71530
00B71A10
6FFE00
6FFDF0
6FFDE0
16
"Tabletennis" object delete, 2 left
"Baseball" object delete, 1 left
"Tabletennis" object delete, 0 left