int string_replase(string &s1, const string &s2, const string &s3)
{
	string::size_type pos = 0;
	string::size_type a = s2.size();
	string::size_type b = s3.size();
	while ((pos = s1.find(s2,pos)) != string::npos)
	{
		s1.replace(pos, a, s3);
		pos += b;
	}
	return 0;
}
string s2 = "###ip##";
string s1 = "http://123###ip##678.com";
string s3 = "192";	
string_replase(s1, s2, s3);
 

//第二種替換字串的方法用erase()和insert()

void string_replace_2(string&s1,const string&s2,const string&s3)
{
	string::size_type pos=0;
	string::size_type a=s2.size();
	string::size_type b=s3.size();
	while((pos=s1.find(s2,pos))!=string::npos)
	{
		s1.erase(pos,a);
		s1.insert(pos,s3);
		pos+=b;
	}
}