leetcode Reverse Words in a String

Given an input string, reverse the string word by word.

For example,

Given s = "

the sky is blue

",

return "

blue is sky the

".

click to show clarification.
Clarification:

What constitutes a word?

A sequence of non-space characters constitutes a word.
Could the input string contain leading or trailing spaces?

Yes. However, your reversed string should not contain leading or trailing spaces.
How about multiple spaces between two words?

Reduce them to a single space in the reversed string.

class Solution {
public:
void reverseWords(string &s) {
int length = s.size();
int ptr=0;
stack<char> str;
stack<char> tmp;
while(s[ptr]==' '&&ptr<length){
ptr++;
}
while(ptr<length){
str.push(s[ptr]);
ptr++;
}
s="";
while(!str.empty()&&str.top()==' '){str.pop();}
if(!str.empty()){
while(true){
char tp = str.top();
tmp.push(tp);
str.pop();
if(str.empty()){
while(!tmp.empty()){s+=tmp.top();tmp.pop();}
break;
}
while(str.top()==' '){
str.pop();
if(str.top()==' '){continue;}
while(!tmp.empty()){s+=tmp.top();tmp.pop();}
s+=' ';
}
}
}
}
};

去掉中间的空格其实我还没有相同，但乱改通过了，还有VS2012运行结果和OJ运行结果不一致是怎么回事呢？