#include  <string>   
#include  <iostream>   
using  namespace  std;   
string&  replace_all(string&  str, const string& old_value, const string& new_value)   
{   
  while(true)  
  {   
    string::size_type  pos(0);   
    if(  (pos=str.find(old_value)) != string::npos  )   
     { 
   str.replace(pos,old_value.length(),new_value); 
 }  
    else { break; }
  }   
  return  str;   
}   

string&  replace_all_distinct(string&  str, const string& old_value, const  string&  new_value)   
{   
  for(string::size_type  pos(0);  pos!=string::npos;  pos+=new_value.length()) 
  {   
    if(  (pos=str.find(old_value,pos)) != string::npos  )   
     { 
   str.replace(pos,old_value.length(),new_value); 
 }  
    else { break; }  
  }   
  return  str;   
}   

int  main()   
{   
  cout  <<  replace_all(string("12212"),"12","21")  <<  endl;   
  cout  <<  replace_all_distinct(string("12212"),"12","21")  <<  endl;   
}   
/* 
输出如下:  
22211  
21221 
*/