#include
#ifndef STRINGBAD_H_
#define STRINGBAD_H_
class StringBad
{
private:
char * str;
int len;
static int num_strings; //不能在类声明中初始静态成员变量 这是因为声明描述如何分配内存 但并不分配内存
public:
StringBad(const StringBad & st); //复制构造函数
StringBad(const char * s); //显示构造函数
StringBad(); //默认构造函数
~StringBad(); //析构函数
friend std::ostream & operator<<(std::ostream & os, const StringBad & st); //友元函数 重载<<运算符
StringBad & operator=(const StringBad & st); //重载赋值运算符
};
#endif
#include
#include"stringbad.h"
using std::cout;
using std::endl;
int StringBad::num_strings = 0; //初始化类静态成员 静态类成员可以在类声明之外只用单独语句进行初始化
StringBad::StringBad(const StringBad & st) //赋值构造函数 进行深度复制
{
num_strings++; //更新静态成员
const int b=len = st.len; //复制私有整型成员
str = new char[len + 1]; //把指针指向创建的新地址
strcpy_s(str, strlen(st.str)+1, st.str); //然后将字符串副本复制到新地址
cout << num_strings << ": \"" << str
<< "\" object created\n";
cout << &str << endl;
} //浅复制导致的结果是把指针（指向同一内存字符串的地址）复制过去 当析构函数调用的时候将释放同一字符串 引起非常严重的后果
//所以 可能会被析构两次 应当使用上述的深度复制 而不是系统默认的
StringBad::StringBad(const char * s)
{
len = std::strlen(s); //检测计算字符串长度 但不包括末尾的空字符 并对len成员进行初始化
str = new char[len + 1]; //创建动态类成员 使用new分配足够的空间保存字符串 然后将新地址赋给str成员
strcpy_s(str, strlen(s) + 1, s); //复制字符串 将第二个字符串拷贝到第一个字符串的位置
num_strings++;
cout << num_strings << ": \"" << str
<< "\" object created\n";
cout << &str << endl;
}
StringBad::StringBad()
{
len = 4;
str = new char[4];
strcpy_s(str, 4, "C++");
num_strings++;
cout << num_strings << ": \"" << str
<< "\" default object created\n";
cout << &str << endl;
}
StringBad::~StringBad()
{
cout << "\"" << str << "\" object deleted, ";
--num_strings;
cout << num_strings << " left\n";
delete[]str;
cout << str << endl;
}
std::ostream & operator<<(std::ostream & os, const StringBad & st)
{
os << st.str;
return os;
}
StringBad & StringBad::operator=(const StringBad & st)
{
if (this == &st) //检测是否自我复制
return *this; //是的话返回并结束
delete[]str; //否则释放str 释放目前占用的内存 因为 指针会等系会指向新内存 所以这段会被浪费掉
len = st.len; //赋值私有成员 无影响
str = new char[len + 1]; //创建新内存 并把新内存地址赋给指针str 因为之前的指向的旧地址已经被释放了 所以节省了内存
strcpy_s(str, strlen(st.str) + 1, st.str); //赋值字符串到新内存当中
return *this; //并返回对象
}
#include
using std::cout;
#include"stringbad.h"
void callme1(StringBad &);
void callme2(StringBad);
int main()
{
using std::endl;
{
cout << "Starting an inner block.\n"; //
StringBad headline1("Celery Stalks at Midnight"); //
StringBad headline2("Lettuce Prey");
StringBad sports("Spinach Leaves Bowl for Dollars");
cout << "headline1: " << headline1 << endl;
cout << "headline2: " << headline2 << endl;
cout << "sports: " << sports << endl;
callme1(headline1);
cout << "headline1: " << headline1 << endl;
callme2(headline2);
cout << "headline2: " << headline2 << endl;
cout << "Initialize one object to another:\n";
StringBad sailor = sports;
cout << "sailor: " << sailor << endl;
cout << "Assign one object to another:\n";
StringBad knot;
knot = headline1;
cout << "knot: " << knot << endl;
cout << "Exiting the block.\n";
}
cout << "End of main()\n";
return 0;
}
void callme1(StringBad & rsb)
{
cout << "String passed by reference:\n";
cout << " \"" << rsb << "\"\n";
}
void callme2(StringBad sb)
{
cout << "String passwd by value:\n";
cout << " \"" << sb << "\"\n";
}
