冗余构造

#include<iostream>
#include <string>
#include<time.h>
using namespace std;
class SuperString{
private:
    char *str;
public:
    SuperString(const char *s=0):str(0){
        if(s!=0){
            str=new char[strlen(s)+1];
            strcpy(str,s);
        }
    }
    SuperString(const SuperString& s):str(0){
        if(s.str){
            str=new char[strlen(s.str)+1];
            strcpy(str,s.str);
        }
    }
    SuperString& operator=(const SuperString& s){
        if(str!=s.str){
            delete[] str;
            if(s.str){
                str=new char[strlen(s.str)+1];
                strcpy(str,s.str);
            }
            else
                str=0;
        }
        return *this;
    }
  ~SuperString(){delete[] str;}
};
class Person{
private:
    SuperString name;
public:
    Person(const char* s){
        name=s;
    }
};
class PersonTwo{
private:
    SuperString name;
public:
    PersonTwo(const char* s):name(s){
    }
};
int _tmain(int argc, _TCHAR* argv[])
{
    clock_t start,finish;
    double totaltime;
    start=clock();
    for(int i=0;i<10000;i++)
    {
        Person p("test");
    }
    finish=clock();
    totaltime=(double)(finish-start)/CLOCKS_PER_SEC;
    cout<<"\nTest 1="<<totaltime<<"秒！"<<endl;

    start=clock();
    for(int i=0;i<10000;i++)
    {
        PersonTwo p("test");
    }
    finish=clock();
    totaltime=(double)(finish-start)/CLOCKS_PER_SEC;
    cout<<"\nTest 2="<<totaltime<<"秒！"<<endl;
    system("pause");
    return 0;
}

运行结果：

Test 1=0.063秒！

Test 2=0.015秒！

Person p("test"); 调用两次SuperString(const char *s=0)和一次SuperString& operator=(const SuperString& s)，两次 ~SuperString()

PersonTwo p("test"); 调用一次SuperString(const char *s=0)，一次 ~SuperString()