分割字符串，保存到容器中
vector<string> str_split(string str,string pattern)
{
std::string::size_type pos;
std::vector<std::string> result;
str+=pattern;//扩展字符串以方便操作
size_t size = str.size();
for(int i=0; i< (int)size; i++)
{
pos = str.find(pattern,i);
if(pos < size)
{
std::string s=str.substr(i,pos-i);
result.push_back(s);
i=pos+pattern.size()-1;
}
}
return result;
}