如何在C中忽略txt文件的特定部分

Question

我的问题是是否可以忽略稍后使用fscanf() 存储在结构中的 txt 文件的特定部分。 出于示例的目的，让我说我有一个由以下文本组成的 txt 文件：

Title: C Programming Language
Author: Dennis Ritchie
Publication year: 1978
...

我想将数据存储在这样的结构中，忽略Title:、Author:、Publication year: 等字样：

struct book {
    char title[MAX];
    char author[MAX];
    int pubblication_year;
    ...
};

这是我为了存储数据而实现的代码：

fscanf(fp, "%[^\n]%*c\n", newOne->books.title);  //titolo
fscanf(fp, "%[^\n]%*c\n", newOne->books.author); //autore
fscanf(fp, "%d\n", &newOne->books.pubblication_year); //anno pubblicazione
...

这里是一个简单的例子：

#include <stdio.h>
#include <stdlib.h>
#define MAX 30
struct book {
    char title[MAX];
    char author[MAX];
};

struct booklist {
    struct book books;
    struct booklist *next;
};


int main() {
    struct booklist *head = NULL, *newOne, *temp; //temp made in order to clear the heap once the program is termined
    FILE *fp;
    fp = fopen("FileName.txt", "r");
    if(fp == NULL) {
    printf("Something wrong happened, the program will close!\n");
        system("pause");
        exit(1);
    } else {
        newOne = (struct booklist *)malloc(sizeof(struct booklist));
        if(newOne == NULL) {
            printf("Error, not enough space to store the new book, the program will close!\n");
                   system("Pause");
                   exit(1);
        }
        fscanf(fp, "%[^\n]%*c\n", newOne->books.title);  //ADDING THE TITLE TO THE NODE
        fscanf(fp, "%[^\n]%*c\n", newOne->books.author); //SAME FOR THE AUTHOR

        //adding the new one node created to the head of the list
        newOne->next = head;
        head = newOne;
    }
    while (newOne != NULL) { //cleaning the heap once the program is termined
    temp = newOne;
    newOne = newOne -> next;
    free(temp);
    }
    fclose(fp);
    return 0;
}

有没有可能？

Answer 1

使用fscanf

char str[] = "Title: C Programming Language";
int len1 = strlen(str); // find length of str

char ch = ':';
char *ret;

ret = strchr(str, ch); // ret points to ---> : C Programming Language
int len2 = strlen(ret);

fseek(fp, (len1-len2), SEEK_SET); // move file pointer
fscanf(fp, "%[^\n]%*c", newOne->books.title);

不使用fscanf

你可以使用strchr()函数。

char str[] = "Title: C Programming Language";
char ch = ':';
char *ret;

ret = strchr(str, ch); 
printf("%s", ret+1) // prints C Programming Language

Answer 2

有一些方法可以为此使用格式字符串。这是一个完全可行的选择。但最简单的方法大概是这样的：

fscanf(fp, "%[^\n]%*c\n", newOne->books.title);
char remove[] = "Title: ";
size_t size = sizeof (remove);
char *s = newOne->books.title;
memove(s, s[size], size);

没有测试上面的代码。可能是小错误。

Answer 3

你的问题的问题是你没有清楚地定义你想让你的程序做什么。

首先，您应该明确说明您的目标。鉴于此文件：

Title: C Programming Language
Author: Dennis Ritchie

Title: The Lord of the Rings
Author: John Ronald Reuel Tolkien

Title: War and Peace
Author: Leo Tolstoy

它应该阅读“C Programming Language”和“Dennis Ritchie”，然后是其余的。但是“标题：”后面的空格是强制性的吗？可以有多个空间吗？标题和作者之间可以有“空”行吗？是否必须具有“标题：”？ “作者”可以在“标题”之前吗？等等……在你定义了所有这些之后，你就有了一个文件格式，也许你可以用 fscanf 解析它。

在这种情况下，如果格式是

<0 or more whitespaces> Title: <0 or more whitespaces> <anything but newline> <newline>

你可以解析它：

fscanf(fp, " Title: %[^\n]", /*...*/);

这要求在标题本身之前存在字符Title:。如果缺少这些，它将失败。

然后，由于您的缓冲区大小有限（一个非常糟糕的主意），建议限制 fscanf() 尝试放入变量的最大字符数（我假设您有一个 31 个字符的数组):

fscanf(fp, " Title: %30[^\n]", tmp->books.title);

用宏做这件事很痛苦，但可以做到。所以你可以像这样读取那个文件：

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

#define xstr(s) str(s)
#define str(s) #s

#define MAX 30
struct book {
    char title[MAX + 1];
    char author[MAX + 1];
};

struct booklist {
    struct book books;
    struct booklist *next;
};
struct booklist *new_booklist(void)
{
    struct booklist *newOne = malloc(sizeof(struct booklist));
    if (newOne == NULL) {
        printf("Error, not enough space to store the new book, the program will close!\n");
        exit(1);
    }
    return newOne;
}
void booklist_add(struct booklist **head, struct booklist *newOne)
{
    newOne->next = *head;
    *head = newOne;
}
void booklist_delete_list(struct booklist **head)
{
    struct booklist *cur = *head;
    while (cur != NULL) {
        struct booklist *temp = cur;
        cur = cur->next;
        free(temp);
    }
    *head = NULL;
}

int main(void)
{
    struct booklist *head = NULL; 
    
    FILE *fp = fopen("input.txt", "r");
    if (fp == NULL) {
        printf("Something wrong happened, the program will close!\n");
        exit(1);
    }

    while(1) {
        struct booklist *tmp = new_booklist();

        int n = 0;
        n += fscanf(fp, " Title: %" xstr(MAX) "[^\n]", tmp->books.title);
        n += fscanf(fp, " Author: %" xstr(MAX) "[^\n]", tmp->books.author);

        if (n != 2) {
            free(tmp);
            break;
        }

        booklist_add(&head, tmp);
    }

    booklist_delete_list(&head);

    fclose(fp);
    return 0;
}

好吧，也许最好将sprintf() 设置为格式变量并将其用作格式字符串，但我不喜欢这两种解决方案中的任何一种。最好的办法可能是使用类似 POSIX getline()