将文本文件扫描到链接列表中 [英] Scanning in a text file into a linked list

问题描述

我只是在学习链表，我必须做一个包含很多部分的作业，但我还是从头开始，我要做的第一件事就是将输入文件读入链表.该文件的一部分是:

乔治·华盛顿(George Washington)，2345678约翰·亚当斯(John Adams)，3456789托马斯·杰斐逊(Thomas Jefferson)，4567890詹姆斯·麦迪逊(0987654)詹姆斯·梦露，9876543约翰·昆西·亚当斯(John Quincy Adams)，8765432

总共包含26行.

我现在要做的只是在文件中读取.我尝试使用此代码(目前主要使用)

  #include< stdio.h>#include< stdlib.h>结构节点{字符名称[20];int id;struct节点* next;}*头;int main(void){结构节点* temp;temp =(结构节点*)malloc(sizeof(结构节点));头=温度;文件* ifp;ifp = fopen("AssignmentOneInput.txt"，"r");int c = 0;而(c< 26){fscanf(ifp，％s"，& temp->名称);fscanf(ifp，％d"，& temp-> id);printf(％d \ n"，c);temp = temp-> next;c ++;} 

对于输出，我知道已扫描了名字和第一个ID，因为c的值显示为0(现在我随意使用c的值来控制fscanf).但是在那之后，程序崩溃了.因此问题必须出在 temp = temp-> next; 上.

我对链表非常陌生，所以我真的不知道自己在做什么.

感谢您的帮助！

解决方案

首先，由于您是用 C 编写的，因此无需强制转换 malloc .

第二，您必须自己为每个新节点分配内存.

第三，数组的名称已经衰减为指针，因此您不应该使用它的& ，因为那样的话，您将得到一个指向您不想要的指针的指针.

最后，您需要修复 scanf 语法以处理字段中的空格.

  #include< stdio.h>#include< stdlib.h>#include< string.h>结构节点{字符名称[20];int id;struct节点* next;}*头;int main(void){结构节点* temp;temp = malloc(sizeof(结构节点));temp-> next = NULL;头=温度;文件* ifp;ifp = fopen("AssignmentOneInput.txt"，"r");int c = 0;字符缓冲区[1024];memset(缓冲区，0，1024);而(c< 5){fgets(缓冲区，1024，ifp);sscanf(缓冲区，％19 [^，]，％d"，临时名称，& temp-> id);printf(％d％s％d \ n"，c，temp->名称，temp-> id);temp-> next = malloc(sizeof(结构节点));temp = temp-> next;temp-> next = NULL;c ++;}} 

I'm just learning about linked lists and I have to do an assignment that has many parts, but I'm starting out and the very first thing I need to do is read in an input file into a linked list. Part of the file is:

George Washington, 2345678 John Adams, 3456789 Thomas Jefferson, 4567890 James Madison, 0987654 James Monroe, 9876543 John Quincy Adams, 8765432

and contains a total of 26 lines.

All I want to do now is simply read in the file. I try by using this code (in main for now)

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


struct node{

    char name[20];
    int id;
    struct node *next;

}*head;



int main(void){

    struct node *temp;
    temp = (struct node *)malloc(sizeof(struct node));
    head = temp;

    FILE *ifp;
    ifp = fopen("AssignmentOneInput.txt", "r");

    int c = 0;

    while(c<26){
        fscanf(ifp, "%s", &temp->name);
        fscanf(ifp, "%d", &temp->id);
        printf("%d\n", c);
        temp = temp->next;
        c++;
    }

For the output, I know that the first name and the first ID are scanned in, because the value of c is displayed as 0 (right now I'm arbitrarily using the value of c to control the fscanf). But after that, the program crashes. So the problem must be with temp = temp->next; It compiles fine.

I am very new to linked lists, so I really don't know what I'm doing.

Your help is appreciated!

解决方案

First of all, since you are writing in C, there's no need to cast the malloc.

Second, you must allocate memory for each new node yourself.

Third, the name of an array already decays to a pointer, so you should not take & of it because then you'll get a pointer to a pointer which is not what you want.

Finally,you need to fix your scanf syntax to handle spaces in your fields.

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

#include <string.h>

struct node{

    char name[20];
    int id;
    struct node *next;

}*head;



int main(void){

    struct node *temp;
    temp = malloc(sizeof(struct node));
    temp->next = NULL;
    head = temp;

    FILE *ifp;
    ifp = fopen("AssignmentOneInput.txt", "r");

    int c = 0;

    char buffer[1024];
    memset(buffer, 0, 1024);
    while(c<5){
        fgets(buffer, 1024, ifp);
        sscanf(buffer, "%19[^,], %d", temp->name, &temp->id);
        printf("%d %s %d\n",c, temp->name, temp->id);
        temp->next = malloc(sizeof(struct node));
        temp = temp->next;
        temp->next = NULL;
        c++;
    }
}

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