c++判定中文字长度

int main()
{
    string s = "高速公路大撞车";
    string result;
    unsigned int i = 0;
    int j = 0;
    while(i < s.size() && j < 6)
    {
        if(s[i] < 255 && s[i] > 0)
        {
            if(j == 5 && i == s.size() - 1)
            {
                result.append(s.substr(i,1));
                break;
            }
            else if(j == 5 && i < s.size() - 1)
            {
                result.append("...");
                break;
            }
            result.append(s.substr(i,1));
            //result.append(" ");
            i++;
            j++;
        }
        else
        {
            if(j == 5 && i == s.size() - 2)
            {
                result.append(s.substr(i,2));
                break;
            }
            else if(j == 5 && i < s.size() - 2)
            {
                result.append("...");
                break;
            }
            result.append(s.substr(i,2));
            //result.append(" ");
            i += 2;
            j++;
        }
    }
    cout<<result<<endl;
    system("pause");
}