如何将字符串倒置

将一句话里的单词进行倒置，标点符号不倒换。比如一句话“i come from tianjin."倒换后变成"tianjin. from come i"。

#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
	cout<<"please input your data"<<endl;
	string str;
    getline(cin,str);
	vector<string> substrs;
	int i,len=str.length(),j,k;
	for(i=0,j=0;i<len;i++)
	{
		if(str.at(i)==' ')
		{
			substrs.push_back(str.substr(j,i-j));
			j=i+1;
		}
	}
	substrs.push_back(str.substr(j,i-j));
	string str1;
	for(k=substrs.size()-1;k>0;k--)
	{
		substrs[k]+=" ";
		str1+=substrs[k];
	}
	str1+=substrs[k];
	cout<<str1<<endl;
}