删除c中通过引用传递的节点

Question

请我尝试删除一个按值传递并由函数返回的节点，但头部是通过引用传递的。我尝试了这段代码，但编译器抱怨： *head = *head->next;

代码如下：

#include<stdio.h>


typedef struct nody student;


struct nody{

    char name[20];

    double gpa;

    student *next;

};

student* deletefirstlist(student **head, student *nn);

int main(){

    student *head, *node, *w;

    node = (student*) malloc(sizeof(student));
    gets(node->name);
    node->gpa=3.6;
    node->next=NULL;

    head = node;

    node = (student*) malloc(sizeof(student));
    gets(node->name);
    node->gpa=3.7;
    node->next=head;

    head = node;

    w = head;
    while(w!=NULL){
        printf("%s %lf\n\n", w->name, w->gpa);
        w=w->next;
    }
    node = deletefirstnode(&head,  node);

    while(w!=NULL){
        printf("%s %lf\n\n", w->name, w->gpa);
        w=w->next;
    }
    return 0;
}

student* deletefirstlist(student **head, student *nn){


    nn = *head;
    *head = *head->next; // the problem is here
    nn->next=NULL;

    return nn;
}

感谢一百万

Answer 1

从引用的代码中，我了解到您创建了一个带有头和链接节点的列表，然后您尝试删除第一个（头）节点。如果是这样，那么 您的代码必须更正为以下内容：

   #include<stdio.h>


    typedef struct nody student;


     struct nody{

       char name[20];

       double gpa;

       student *next;

     };

   student *deletefirstnode(student *head, student *nn);

   int main(){

    student *head, *node, *w;

    node = (student*) malloc(sizeof(student));
    gets(node->name);
    node->gpa=3.6;
    node->next=NULL;

    head = node;

    node = (student*) malloc(sizeof(student));
    gets(node->name);
    node->gpa=3.7;
    head->next=node;
    node->next=NULL;

    //  head->next = node (The first node is the head node)

    w = head;
    while(w!=NULL){
     printf("%s %lf\n\n", w->name, w->gpa);
     w=w->next;
    }
    node = deletefirstnode(head,  node);
    free(head); //to free up the memory of the old first node
    w=node;  //reset w to point to the new First node of the list
    while(w!=NULL){
     printf("%s %lf\n\n", w->name, w->gpa);
     w=w->next;
     }
    return 0; 
   }

   student *deletefirstnode(student *head, student *nn){
      nn = head->next;
      return nn;
   }

希望这些帮助。

Answer 2

整体校正样本

#include <stdio.h>
#include <stdlib.h> //need this

typedef struct nody student;

struct nody{
    char name[20];
    double gpa;
    student *next;
};

student* deletefirstlist(student **head, student *nn);

int main(){
    student *head, *node, *w;

    node = (student*) malloc(sizeof(student));//casting is not necessary in C.
    *node->name = 0;
    //gets has already been abolished.
    while(1 != scanf("%19[^\n]%*c", node->name)){
        printf("input name\n");
        scanf("%*[^\n]");scanf("%*c");
    }
    node->gpa=3.6;
    node->next=NULL;

    head = node;

    node = (student*) malloc(sizeof(student));
    *node->name = 0;
    while(1 != scanf("%19[^\n]%*c", node->name)){
        printf("input name\n");
        scanf("%*[^\n]");scanf("%*c");
    }
    node->gpa=3.7;
    node->next=head;

    head = node;

    w = head;
    while(w != NULL){
        printf("%s %lf\n\n", w->name, w->gpa);
        w = w->next;
    }
    node = deletefirstlist(&head,  NULL);//The argument node is not necessary substantially. also function name is typo.

    free(node);

    w = head;//you forgot this
    while(w != NULL){
        printf("%s %lf\n\n", w->name, w->gpa);
        w = w->next;
    }
    //free rest
    return 0;
}

student* deletefirstlist(student **head, student *nn){
    nn = *head;
    if(*head){//NOT NULL
        *head = (*head)->next; // *head->next meant *(head->next)
        nn->next=NULL;
    }

    return nn;
}

Answer 3

考虑到编译器抱怨，这将解决它

*head = (*head)->next;

但是代码还有其他问题，例如您没有为函数返回的已删除节点释放内存：

node = deletefirstnode(&head,  node);
free(node); //missing
w=head; //w still points to the deleted node, point it to the new head 
while(w!=NULL){

BLUEPIXY 的代码解决了所有这些问题。

如果你使用 C++，我可以建议使用字符串作为名称，那么你可以轻松地将输入作为

getline(cin,name);

你也可以将你的函数用作

student* deletefirstlist(student*& head, student *nn);

那么就不需要使用间接了。你可以简单地做：

student* deletefirstlist (student* &head, student *nn) {
nn = head;
if (head) {
    head = head->next; // *head->next meant *(head->next)
    nn->next=NULL;
}

return nn;
}

并调用：

node = deletefirstlist(head, node);

您也需要更改 fn 声明：

student* deletefirstlist(student *&head, student *nn);