插入有序列表时出错

Question

我意识到函数插入动态有序列表，但我不明白为什么它不起作用:(我必须列出手机类，我必须为字母数字代码订购

template<class T>
void lista<T>::insord(T &val) {
    nodo<T> *newptr = getnew(val);
    nodo<T> *p = firstptr;
    nodo<T> *prec = firstptr;        

    if(isempty())
        firstptr = lastptr = newptr;
    else {
        // while ((p->nextptr != 0) &&
        //        ((p->data->getnumtel()) > (newptr->data->getnumtel())))

        while ((p->nextptr != NULL) &&
               (strcmp(p->data->getcod(), newptr->data->getcod()) > 0)) {
           prec = p;
           p=p->nextptr;
        }

        if (p->nextptr != NULL) {
            // if ((p->data->getnumtel())==(newptr->data->getnumtel()))

            if (strcmp(p->data->getcod(),newptr->data->getcod()) == 0)
               throw ecc();
            newptr->nextptr = p;
            prec->nextptr = newptr;
        } else {
            lastptr->nextptr = newptr;
            newptr->nextptr = NULL;
            lastptr = newptr;
        }
    }
}