C 在链表开头插入元素

Question

我用 C 编写了一个程序，旨在将结构按升序插入链表。

问题是没有插入我的两个最低值(1 和 2)。这是因为我目前没有工作处理程序来检查链表的第一个值是否已经大于给定值。

这是我的功能:

struct PCB
{
    struct PCB *Next_PCB ;
    int PID ;
};

void insert_ordered (struct PCB *Head, struct PCB *Add)
{
    tmp = Head;
    if (Head->PID == 0) {
        Head->PID = Add->PID;
    } else {
        if (Head->Next_PCB == NULL) {
            Head->Next_PCB = Add;
        } else {
            int count = 0;
            while (Head != NULL) {
                if (Add->PID > Head->PID) {
                    if (Head->Next_PCB != NULL) {
                        Head = Head->Next_PCB;
                        count++;
                    } else {
                        Head->Next_PCB = Add;
                        break;
                    }
                } else if (Add->PID == Head->PID) {
                    Add->Next_PCB = Head->Next_PCB;
                    Head->Next_PCB = Add;
                    break;
                } else if (Add->PID < Head->PID) {
                    if (Add->PID == 1 || Add->PID == 2) {
                        printf("found 1 or 2");
                        printf("count: %d", count);
                    }
                    int ct = 0;
                    while (tmp != NULL) {
                        if (count == 0) {
                            printf("made it, %d", ct);
                            Add->Next_PCB = tmp;
                            break;
                        } else if (ct == (count - 1)) {
                            Add->Next_PCB = Head;
                            tmp->Next_PCB = Add;
                            break;
                        }
                        tmp = tmp->Next_PCB;
                        ct++;
                    }
                    break;
                }
            }
        }
    }
    printf("pid : %d\n", Add->PID);
}

这是打印列表后的输出:

pid : 6
pid : 17
pid : 15
pid : 13
pid : 15
pid : 6
pid : 12
pid : 9
found 1 or 2count: 0made it, 0pid : 1
found 1 or 2count: 0made it, 0pid : 2
pid : 7
pid : 10
pid : 19

-------------------
PID: 6
PID: 6
PID: 7
PID: 9
PID: 10
PID: 12
PID: 13
PID: 15
PID: 15
PID: 17
PID: 19

输出应该在两个 6 之前有一个 1 和一个 2。有人可以帮帮我吗？谢谢。

Answer 1

void insert_ordered (struct PCB *Head, struct PCB *Add):无法替换此界面中元素的头部。所以，你需要在dummy elements中的第一个元素(Anchor node that are not intended contents of holding)。
下面是一个具体的例子:

#include <stdio.h>
#include <stdlib.h>

struct PCB{
    struct PCB *Next_PCB ;
    int PID ;
};

struct PCB *new_PCB(int PID){
    struct PCB *pcb = malloc(sizeof(*pcb));
    if(pcb != NULL){
        pcb->Next_PCB = NULL;
        pcb->PID = PID;
    }
    return pcb;
}

void insert_ordered (struct PCB *Head, struct PCB *Add){
    if(Head == NULL)
        return ;//can't

    struct PCB *prev = Head, *curr = Head->Next_PCB;
/*  this is reduced to following while-loop
    if(Head->Next_PCB == NULL){//empty list
        Head->Next_PCB = Add;
        return ;
    }
    if(Add->PID <= curr-> PID){//Add node <= Top node
        prev->Next_PCB = Add;
        Add->Next_PCB = curr;
        return ;
    }
*/
    while(curr != NULL && curr->PID < Add->PID){
        prev = curr;
        curr = curr->Next_PCB;
    }
    prev->Next_PCB = Add;
    Add->Next_PCB = curr;
}

void print(struct PCB *Head){
    if(Head == NULL)
        return ;
    else
        Head = Head->Next_PCB;
    while(Head != NULL){
        printf("PID: %d\n", Head->PID);
        Head = Head->Next_PCB;
    }
}

//alias
#define Make_list() new_PCB(-1)

int main(void){
    struct PCB *head = Make_list();
    //struct PCB *head = new_PCB(-1);//dummy node, This is intended to holds a list.
    insert_ordered (head, new_PCB( 6));
    insert_ordered (head, new_PCB(17));
    insert_ordered (head, new_PCB(15));
    insert_ordered (head, new_PCB(13));
    insert_ordered (head, new_PCB(15));
    insert_ordered (head, new_PCB( 6));
    insert_ordered (head, new_PCB(12));
    insert_ordered (head, new_PCB( 9));
    insert_ordered (head, new_PCB( 1));
    insert_ordered (head, new_PCB( 2));
    insert_ordered (head, new_PCB( 7));
    insert_ordered (head, new_PCB(10));
    insert_ordered (head, new_PCB(19));

    print(head);
    //release list
    return 0;
}

或者您需要像排序一样交换内容。