C++ Display longest word of the string and its length using vectors and string functions

The task is to find the longest word and its length in the string. I know the other way to solve this problem, but I want to try it this way.
The string is "abra cadabra fibra" (cadabra 7 is an answer).
Thank you.

using namespace std;

vector<int> spacesPosititons(string s){
    vector<int> positions;
    int pos = s.find(' ');

    while(pos != string::npos){
        positions.push_back(pos);
        pos = s.find(' ',pos+1);
    }

    return positions;
}
int main(){

    //freopen("input.txt","r",stdin);

    string str,word;
    getline(cin,str);

    str = " " + str + " ";

    int max = 0;

    vector<int> temp = spaces(str);
    vector<int> diff;

    for(int i = 0; i < temp.size(); ++i){
        diff.push_back(temp[i+1]-temp[i]);
    }

    for(int i = 0; i < diff.size(); ++i){
        if(diff[i] > max){
            max = diff[i];                  
        }
    }

    for(int i = 0; i < temp.size(); ++i){
        if(temp[i+1]-temp[i] == max){
            word = str.substr(temp[i]+1,max-1);     
        }
    }
    cout << word << endl << word.size();


    return 0;
}