//strquote.cpp -- different designs
#include <iostream>
#include <string>
using namespace std;
string version1(const string & s1,const string & s2);
const string & version2(string & s1,const string & s2);  //has side effect
const string & version3(string & s1,const string & s2);  //bad design

int main()
{
   string input;
   string copy;
   string result;
   
   cout<<"Enter a string: ";
   getline(cin,input);
   copy=input;
   cout<<"Your string as entered: "<<input<<endl;
   result=version1(input,"***");
   cout<<"Your string enhanced: "<<result<<endl;
   cout<<"Your original string: "<<input<<endl;
   
   result=version2(input,"###");
   cout<<"Your string enhanced: "<<result<<endl;
   cout<<"Your original string: "<<input<<endl;
   cout<<"Resetting original string.\n";
   input=copy;
   result=version3(input,"@@@");
   cout<<"Your string enhanced: "<<result<<endl;
   cout<<"Your original string: "<<input<<endl;
   
   system("pause");
   return 0;
   
}

string version1(const string & s1,const string &s2)
{
       string temp;
      
       temp=s2+s1+s2;;
       return temp;
       }
      
const string & version2(string & s1,const string & s2)
{
      s1=s2+s1+s2;
      return s1;
      }

const string & version3(string & s1,const string & s2)       //这个函数的错误在哪里?
{                                                            //书上说存在一个致命的错误:返回一个指向version3()中声明的变量的引用.具体的说,
                                                            //问题是由于下面的复制语句引发的:result=version3(input,"@@@");程序试图引用已经
                                                            //释放的内存
                                                            //不明白????高手能详细解释一下吗?
       string temp;
      
       temp=s2+s1+s2;;
       return temp;
       }

[[it] 本帖最后由 tymstill 于 2008-4-17 16:31 编辑 [/it]]

那跟第一个string version1(const string & s1,const string &s2)
{
       string temp;
      
       temp=s2+s1+s2;;
       return temp;
       }
有什么区别吗?

为什么第一个会产生临时变量,第二个不会呢?是不是前面多了个const呢?