初学C++，关于数据结构的说明？

ListArray_id<Coord> gridlist;

template<class tdata> class ListArray_id {

    class Item {

    public:
        Item* pnext;
        Item* pprev;
        tdata object;
    };


private:
    Item** array;
    Item* pfirstitem;
    Item* plastitem;
    Item* pthisitem;
    unsigned int nseg;
    unsigned int id;
    unsigned int thisobj;

public:
    bool isobj;
    unsigned int nobj;

public:
    ListArray_id() {
        pfirstitem=NULL;
        plastitem=NULL;
        pthisitem=NULL;
        isobj=false;
        nobj=0;
        nseg=0;
        id=0;
    }

    void killall() {
        Item* pitem=pfirstitem;
        Item* pnext;
        while (pitem) {
            pnext=pitem->pnext;
            delete pitem;
            pitem=pnext;
        }
        if (nseg) delete[] array;
        pfirstitem=NULL;
        plastitem=NULL;
        pthisitem=NULL;
        isobj=false;
        nobj=0;
        nseg=0;
        id=0;
    }

    ~ListArray_id() {
        killall();
    }

    void initarray(unsigned int nitem) {
        unsigned int i;
        killall();
        if (nitem<=0) return;
        nseg=nitem%SEGSIZE;
        if (nseg*SEGSIZE<nitem) nseg++;
        array=new Item*[nseg*SEGSIZE];
        if (!array) fail();
        for (i=0;i<nitem;i++) createobj();
        pthisitem=0;
        thisobj=0;
    }

    tdata& createobj() {
        Item* pitem=new Item;
        if (!pitem) fail();
        pitem->object.id=id++;
        pitem->pprev=plastitem;
        pitem->pnext=NULL;
        if (plastitem) plastitem->pnext=pitem;
        else pfirstitem=pitem;
        plastitem=pitem;
        pthisitem=pitem;
        isobj=true;
        thisobj=nobj++;
        if (nobj>nseg*SEGSIZE) {
            Item** newarray=new Item*[(nseg+1)*SEGSIZE];
            if (!newarray) fail();
            if (nseg++) {
                unsigned int i;
                for (i=0;i<nobj-1;i++)
                    newarray[i]=array[i];
                delete[] array;
            }
            array=newarray;
        }
        array[nobj-1]=pitem;
        return pitem->object;
    }

    bool firstobj() {
        if (pfirstitem) {
            pthisitem=pfirstitem;
            isobj=true;
            thisobj=0;
            return true;
        }
        return false;
    }

    bool nextobj() {
        if (pthisitem) {
            pthisitem=pthisitem->pnext;
            thisobj++;
        }
        if (pthisitem) return true;
        isobj=false;
        return false;
    }

    tdata& getobj() {
        return pthisitem->object;
    }

    tdata& operator[](unsigned int i) {
        return array[i]->object;
    }

    void killobj() {
        unsigned int i;
        if (!pthisitem) return;
        if (pthisitem==pfirstitem) pfirstitem=pthisitem->pnext;
        if (pthisitem==plastitem) plastitem=pthisitem->pprev;
        Item* pnextitem=pthisitem->pnext;
        if (pthisitem->pprev) pthisitem->pprev->pnext=pthisitem->pnext;
        if (pthisitem->pnext) pthisitem->pnext->pprev=pthisitem->pprev;
        delete pthisitem;
        pthisitem=pnextitem;
        if (!pthisitem) isobj=false;
        for (i=thisobj+1;i<nobj;i++)
            array[i-1]=array[i];
        nobj--;
    }
};

struct Coord {

    // Type for storing grid cell longitude, latitude and description text

    int id;
    double lon;
    double lat;
    xtring descrip;

};