C 从文件中读取数字并保存在链表中

文件格式：

我必须阅读这些数字，有50行这样的线，以Xvalue的方式。。。。链接列表中的Y值。我读数字有困难。 我创建的链接列表如下所示：

    list L;
    node *p, *q;
    int i;

    L = (list *)malloc(sizeof(node));
    L -> x = L -> y = 0;
    L -> nextx = L -> nexty = NULL;

    FILE *fp;
    fp = fopen("points.txt", "r");
    if (fp == NULL) 
    {
        fprintf(stderr, "Error: unable to open file...\n");
    }

    p = L;
    for (i=0; i<100; ++i) 
    {
        q = (node *)malloc(sizeof(node));
        q -> x =  // store x values here
        q -> y =  // store y values here
        q -> nextx = q -> nexty = NULL;
        p -> nextx = p -> nexty = q;
        p = q;
    }

1您可以使用fscanf从文件中读取整数对。检查返回值以确保fscanf匹配2项

2您的链表处理错误。普通链表只有一个下一个指针

代码可以用多种方式编写。以下是一个例子：

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

typedef struct s_node
{
    int x;
    int y;
    struct s_node* next;
} node;

void print_list(node* p)
{
    printf("List contains:\n");
    while (p)
    {
        printf("x=%d y=%d\n", p->x, p->y);
        p = p->next;
    }
}

node* new_node(int x, int y)
{
    node* p = malloc(sizeof *p);
    assert(p);
    p->x = x;
    p->y = y;
    p->next = NULL;
    return p;
}

void free_list(node* p)
{
    while(p)
    {
        node* tmp = p;
        p = p->next;
        free(tmp);
    }
}

node* read_list(FILE* fp)
{
    int x, y;
    node* head = NULL;
    node* last = head;

    // Repeat reading as long as fscanf matches 2 items
    while(fscanf(fp, "%d %d", &x, &y) == 2)
    {
        if (last)
        {
            // Insert at end of list
            last->next = new_node(x, y);
            last = last->next;
        }
        else
        {
            // Special handling for first element in list
            head = new_node(x, y);
            last = head;
        }
    }
    return head;    
}

int main(void) 
{
    FILE* fp = stdin;  // Here input is taken from standard in
                       // Use:
                       //        fp = fopen("points.txt", "r");
                       //        assert(fp);
                       //
                       // to read from a file

    node* head = read_list(fp);

    print_list(head);

    free_list(head);

    return 0;
}

---

只需fscanffp，%d%d，&q->x，&q->y；？L=列表*mallocsizeofnode；将list*赋值给具有list类型的变量看起来很奇怪。另外，为什么要分配的大小是一个节点，而缓冲区似乎用作列表？顺便问一下，什么是列表和节点？啊，需要检查读取是否成功，因为循环是100次，而文件只包含50行。这就像fscanffp、%d%d、&q->x、&q->y！=2{freeq；break；}。即使在打印错误后，您的程序仍将尝试读取文件：无法打开文件。。。。这将很危险。您需要发布列表和节点的定义。列表L的处理似乎是错误的，同时使用nextx和nexty似乎是错误的。通常，链表只有一个下一个指针。

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

typedef struct s_node
{
    int x;
    int y;
    struct s_node* next;
} node;

void print_list(node* p)
{
    printf("List contains:\n");
    while (p)
    {
        printf("x=%d y=%d\n", p->x, p->y);
        p = p->next;
    }
}

node* new_node(int x, int y)
{
    node* p = malloc(sizeof *p);
    assert(p);
    p->x = x;
    p->y = y;
    p->next = NULL;
    return p;
}

void free_list(node* p)
{
    while(p)
    {
        node* tmp = p;
        p = p->next;
        free(tmp);
    }
}

node* read_list(FILE* fp)
{
    int x, y;
    node* head = NULL;
    node* last = head;

    // Repeat reading as long as fscanf matches 2 items
    while(fscanf(fp, "%d %d", &x, &y) == 2)
    {
        if (last)
        {
            // Insert at end of list
            last->next = new_node(x, y);
            last = last->next;
        }
        else
        {
            // Special handling for first element in list
            head = new_node(x, y);
            last = head;
        }
    }
    return head;    
}

int main(void) 
{
    FILE* fp = stdin;  // Here input is taken from standard in
                       // Use:
                       //        fp = fopen("points.txt", "r");
                       //        assert(fp);
                       //
                       // to read from a file

    node* head = read_list(fp);

    print_list(head);

    free_list(head);

    return 0;
}