调试和释放模式下的结果不同

vector<double> pvec;

double firstnode=0.0;

for(iter2=svec.begin(); iter2!=svec.end(); iter2++)
{
    double price= 0.0;
    string sFiyat = iter2->substr(13);
    stringstream(sFiyat)>>price;
    price=log(price);

    if (iter2==iter)
    {
        firstnode = price;
    }
    price -= firstnode;

    pvec.push_back(price);
}