String类的实现 三大复制控制函数

1.深拷贝

</pre><pre code_snippet_id="1689102" snippet_file_name="blog_20160519_1_1528207" name="code" class="cpp">#include <iostream>
using namespace std;

class String{
public:

  friend ostream& operator<<(ostream& out, const String& str);//友员

  String(const char * str = NULL);// 默认参数
  String(const String &str);
  String& operator=(const String &str);

  ~String();

private:

  ostream& outPut(ostream& out)const;//const
  char *data;
};

String::String(const char* str){
  if (str == NULL){  // 得分点：对空字符串自动申请存放结束标志'\0'的//加分点：对m_data加NULL 判断
    data = new char[1];
    data[0] = '\0';
  }
  else{
    int len = strlen(str);
    data = new char[len + 1];
    strcpy(data, str);
  }
}

String::String(const String& str){ // 得分点：输入参数为const型
  int len = strlen(str.data);
  data = new char[len + 1];
  strcpy(data, str.data);
}

String& String::operator =(const String &str){
  if (this != &str){ //得分点：检查自赋值
    String tmp(str);
    char *tmp_data = tmp.data;
    tmp.data = data;
    data = tmp_data;
  }
  return *this;
}


String::~String(){
  delete[]data;
}


ostream& String::outPut(ostream& out)const{ //const成员函数
  out << data;
  return out;
}

ostream& operator<<(ostream& out, const String& str){//
  return str.outPut(out);
}

int main(){

  char* p = "Hello World !";
  String s(p);
  cout << s << endl;
  String s1("How are you ?");
  cout << s1 << endl;
  
  String s2(s1);
  cout << s2 << endl;

  s = s2;
  cout << s << endl;

  return 0;
}

2.浅拷贝

#include<iostream>
using namespace std;

//模拟new[]，在前面多开4个字节来存引用计数
class String
{
public:
  String(char* str = "")
    :_str(new char[strlen(str) + 5])
  {
    _str += 4;
    _GetRefCount(_str) = 1;
    strcpy(_str, str);
  }

  String(const String& s)
    :_str(s._str)
  {
    ++_GetRefCount(_str);
  }
  String& operator=(const String& s)
  {
    if (_str != s._str)
    {
      _Release();
      _str = s._str;
      ++_GetRefCount(_str);
    }
    return *this;
  }
  

  char& operator[](size_t index)
  {
    if (_GetRefCount(_str) > 1)
    {
      char* tmp = new char[strlen(_str) + 5];
      tmp += 4;
      _GetRefCount(tmp) = 1;
      strcpy(tmp, _str);
      --_GetRefCount(_str);
      _str = tmp;
    }
    return _str[index];
  }


  ~String()
  {
    cout << "~String()" << endl;
    _Release();
  }
  int& _GetRefCount(char* str)
  {
    return(*(int*)(str - 4));
  }
  void _Release()
  {
    if (--(_GetRefCount(_str)) == 0)
    {
      delete[](_str - 4);//指针返回首地址位置，释放整段空间
    }
  }
  void put()
  {
    cout << _GetRefCount(_str) << "---------" << _str << endl;
  }
private:
  char* _str;
};

void Test()
{
  String S;
  String s1 = "abclefg";
  String s2(s1);
  S.put();
  s1.put();
  s2.put();
  s2 = s1;
  s2.put();
  cout << "**********************" << endl;

  String s3 = "hijklmn";
  String s4(s3);
  s3.put();
  s3 = s1;
  s3.put();

  cout << "**********************" << endl;

  s1.put();
  s1[3] = 'd';
  s1.put();
  s2.put();
}

int main()
{
  Test();

  return 0;
}

1---------

2---------abclefg

2---------abclefg

2---------abclefg

**********************

2---------hijklmn

3---------abclefg

**********************

3---------abclefg

1---------abcdefg

2---------abclefg

~String()

~String()

~String()

~String()

~String()