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C: fgets用于构建字符的链接列表*

fgets linked-list c

Ian Zurutuza · 技术社区 · 7 年前

我正在使用 fgets() 错了吗?

char * )将每一新行添加到LL的末尾。我从文件中读取这些行,但由于某种原因,每一行都会被正在处理的当前行覆盖,只有在使用 fgets() 内部 while 循环,但add函数似乎正确地接收了每一行。

main() 没有问题。

下面是一个示例输入文件:

输入txt:

This life, which had been the
tomb of his virtue and of his
honour, is but a walking
shadow; a poor player, that
struts and frets his hour upon
the stage, and then is heard
no more: it is a tale told by an
idiot, full of sound and fury,
signifying nothing.
    --William Shakespeare

代码:

#include <stdio.h> //printf, fopen
#include <stdlib.h> //exit, EXIT_FAILURE
#include <string.h> //strlen

struct node {
    char *line;
    struct node *next;
};

void print(struct node *node);

void add(struct node **head, char *newLine) {
    //printf("%s", newLine);

    struct node *new_node = (struct node *)malloc(sizeof(struct node));
    struct node *curr = *head;

    new_node->line = newLine;
    new_node->next = NULL;

    if (*head == NULL) {
        *head = new_node;
    } else {
        while (curr->next != NULL) {
            curr = curr->next;
        }
        curr->next = new_node;
    }
    print(*head);
}

void print(struct node *node) {
    printf("\n");

    while (node != NULL) {
        printf("%s\n", node->line);
        node = node->next;
    }
}

int main(int argc, char *argv[16]) {
    char newLine[81];
    struct node *head = NULL;
    FILE *fp = fopen(argv[1], "r");

    if (fp == NULL) {
        printf("ERROR: file open failed");
        exit(EXIT_FAILURE);
    }

    while (fgets(newLine, 81, fp)) {
        add(&head, newLine);
    }

    add(&head, "why");
    add(&head, "does");
    add(&head, "this");
    add(&head, "work??");

    fclose(fp);

    print(head);

    return 0;
}

3 回复 | 直到 7 年前

Gambit Support 7 年前

您的问题在于add()方法。它不断向列表添加相同的缓冲区指针。您需要将列表中的缓冲区复制到新分配的空间,即。节点->行也需要进行malloced,并将换行复制到其中。

Some programmer dude 7 年前

你有一 全部的

最简单的解决方案是使节点结构中的字符串成为数组,并将字符串复制到其中。

使用常量字符串文字的区别在于,每个字符串都是不同的数组。

chqrlie 7 年前

您必须为每一行分配内存。按照当前编码,所有节点都指向 main() fgets() .

还要注意,添加到列表中的每一行都包含一个终止换行符,您可能应该在调用之前去掉它。

#include <stdio.h>  // printf, fopen
#include <stdlib.h> // exit, EXIT_FAILURE
#include <string.h> // strlen, strdup

struct node {
    char *line;
    struct node *next;
};

void print(struct node *node);

void add(struct node **head, char *newLine) {
    //printf("%s", newLine);

    struct node *new_node = malloc(sizeof(struct node));
    struct node *curr = *head;

    new_node->line = strdup(newLine);
    new_node->next = NULL;

    if (*head == NULL) {
        *head = new_node;
        return;
    }

    while (curr->next != NULL) {
        curr = curr->next;
    }

    curr->next = new_node;
    print(*head);
}

void print(const struct node *node) {
    printf("\n");

    while (node != NULL) {
        printf("%s\n", node->line);
        node = node->next;
    }
}

int main(int argc, char *argv[16]) {
    char newLine[81];
    struct node *head = NULL;
    FILE *fp = fopen(argv[1], "r");

    if (fp == NULL) {
        printf("ERROR: file open failed");
        exit(EXIT_FAILURE);
    }

    while (fgets(newLine, sizeof newLine, fp)) {
        newLine[strcspn(newLine, "\n")] = '\0'; // strip the newline if present
        add(&head, newLine);
    }

    add(&head, "why");
    add(&head, "does");
    add(&head, "this");
    add(&head, "work??");

    fclose(fp);

    print(head);

    return 0;
}