队列的链式存储---链表实现(有头结点)

/* 队列的链式存储 */
/* with header */
/* with no typedef */
struct Node{
    ElementType Ele;
    struct Node *Next;
};
struct LinQ{
    struct Node *rear;
    struct Node *front;
};
struct LinQ *
CreateQ( void )
{
    struct LinQ *Ptr;
    struct Node *header;
    
    Ptr = malloc(sizeof(struct LinQ));
    if(Ptr == NULL )
        Error("out of space ");
        
    header = malloc( sizeof( struct Node ) );
    if(header == NULL )
        error("out of space ");
        
    header->Next = NULL;
    Ptr->front = Ptr->rear = header;
}
void
AddQ( struct LinQ *PtrQ, ElementType X )
{
    struct Node *Ptr;
    Ptr = malloc(sizeof(struct Node ));
    if(Ptr == NULL)
        Error("out of space ");
    Ptr->Ele = X;
    Ptr->Next = NULL;
    PtrQ->rear->Next = Ptr;
    PtrQ->rear = Ptr; 
}
int
IsEmpty( struct LinQ * PtrQ )
{
    return PtrQ->front->Next == NULL;
}

ElementType
DeleteQ( struct LinQ * PtrQ )
{
    struct Node * TmpCell;
    if( IsEmpty( PtrQ ) )
        Error("empty Queue");
    Tmpcell = PtrQ->front->Next;
    PtrQ->front->Next = TmpCell->Next;
    free( TmpCell );
}

CreateQ旨在创造一个front和rear都指向头结点header的LinQ结构

头结点处Next设为NULL，在判断是否空队时可用

front一直指到头结点

新增结点的Next一定改为NULL

结论：可以用typedef的地方就用，可以用头结点的地方就用