C语言 删除链表中的第一个节点

Question

我的作业有问题，它涉及编辑链表。我的代码似乎工作得很好，除了它不删除学生ID=1(或链表中的第一个节点)的数据项。当我试图删除链表上的第一个节点(或者，在main()中删除(1))时，它返回"学生未找到"消息。有人能告诉我出了什么问题吗?谢谢。

/****************************************************************************  
    Date        : 12 August 2015  
    Assignment  : Use linked list to build a database of student records, which supports find(), insert() and delete()  
    ****************************************************************************/
#include <stdlib.h>
#include <stdio.h>
/* Define structure studentNode that contains ID, name, GPA and pointer to next studentNode*/
typedef struct student {
    int ID;
    char *name;
    float GPA;
    struct student *nextStudentNode;
} studentNode;
/* Initialize header */
studentNode *header;
/* Function prototypes*/
void insert(int ID, char *name, float GPA);
void printList();
void delete(int ID);
/* Main function which runs through while loop until sentinel value of q is typed by user. */
int main() {
    insert(3, "John", 3.5);
    insert(12, "Smith", 2.8);
    insert(1, "Mary", 1.8);
    printList();
    delete(1);    /***** there seems to be a problem here*********/
    delete(12);
    delete(3);
    printList();
    return 0;
}
/* Insert new student data */
void insert(int ID, char *name, float GPA) {
    studentNode *newStudent = (studentNode*)malloc(sizeof(struct student));
    newStudent->ID          = ID;
    newStudent->name        = name;
    newStudent->GPA         = GPA;
    newStudent->nextStudentNode = header; 
    header = newStudent;
}
/* Run through linked list one by one to print all data items */
void printList() {
    studentNode *tempNode;
    for (tempNode = header ; tempNode != NULL ; tempNode = tempNode->nextStudentNode) {
        printf( "ID:%d name:%s GPA:%fn" , tempNode->ID, tempNode->name, tempNode->GPA);
    }
}
/* Delete student data */
void delete(int inputID) {
    studentNode *tempNode;
    studentNode **headerPtr = &header;
    for (tempNode = *headerPtr ;
         tempNode->nextStudentNode->ID != inputID && tempNode->nextStudentNode->nextStudentNode != NULL;
         tempNode = tempNode->nextStudentNode);
    studentNode *nodeToDelete = tempNode->nextStudentNode;
    if (nodeToDelete->ID != inputID) {
        printf("Student not found.n");
    } else {
        printf("ID:%d name:%s GPA:%f is deleted.n" , nodeToDelete->ID, nodeToDelete->name,
               nodeToDelete->GPA);
        tempNode->nextStudentNode = nodeToDelete->nextStudentNode;
        free(nodeToDelete);
    }
}

Answer 1

问题在于:

for( tempNode = *headerPtr ; tempNode->nextStudentNode->ID != inputID && tempNode->nextStudentNode->nextStudentNode != NULL ; tempNode = tempNode->nextStudentNode );

你从第二个学生开始检查，而不是第一个学生。因此，您将在没有找到正确ID的情况下到列表末尾。

:我的意思是订单列表。

Answer 2

函数第一个循环中的条件

tempNode->nextStudentNode->ID != inputID && tempNode->nextStudentNode->nextStudentNode != NULL ;

是错误的，因为它跳过了第一个节点的ID。

函数可以写得更简单

/* Delete student data */
void delete( int inputID )
{
    studentNode *prev = NULL;
    studentNode *tempNode = head;
    while ( tempNode && tempNode->ID != inputID )
    {
        prev = tempNode;
        tempNode = tempNpde->nextStudentNode;
    }
    if ( tempNode )
    {
        if ( !prev ) head = tempNode->nextStudentNode;
        else prev->nextStudentNode = tempNode->nextStudentNode;
        free( tempNode );
    }
}