c - C链表中的内存泄漏

Question

我正在编写一些 C 代码，并尝试使用列表。出于某种原因，以下代码为我提供了本书的作者、年份和 ISBN，但缺少标题。我怀疑这是“insert_at_begin”函数某处的内存泄漏。虽然我真的不确定在那里做什么。该程序从包含书名、作者等的文件中读取，并应将其作为动态列表返回。

任何提示或某种帮助将不胜感激。我确实环顾了互联网和堆栈溢出，但找不到解决此内存泄漏的方法。我添加了相关代码，虽然很长，但我不确定泄漏在哪里，所以我认为这样会更好。

typedef struct _element element;


typedef struct _list { 
    element *first;    
    int count;        
} list;


struct _element {
    char* title;
    char* author;
    int year;
    long long int isbn;
    element *next;
};


element *insert_at_begin(element *first, element *new_elem) {

    if(first) {
        new_elem->next = first;
        first = new_elem;

    } else {
        first = new_elem;
    }

    return first;

}


element *construct_element(char *title, char* author, int year, long long int isbn) {

    element* book = malloc(sizeof(element));
    book->title = title;
    book->author = author;
    book->year = year;
    book->isbn = isbn;
    book->next = NULL;
    return book;
}


void free_list(list *alist) {

    //Only when there is 2 elements in the list start this loops
    for (int i=1; i<alist->count; i++) {
        free(alist->first->next);
    }

    free(alist->first);
    free(alist);

}


void read_list(char* filename, list *alist) {
    element* new_elem;

    char* title;
    char* author;
    int year;
    long long int isbn;
    read_line_context ctx;
    open_file(&ctx, filename);
    while(read_line(&ctx, &title, &author, &year, &isbn) == 0) {
        new_elem = construct_element(title, author, year, isbn);
        alist->first = insert_at_begin(alist->first, new_elem);
        alist->count++;
    }
}

list* construct_list() {
    list *alist = malloc(sizeof(list));
    alist->first = NULL;
    alist->count = 0;
    return alist;
}


void print_list(list *alist) {
    printf("My Books\n================\n\n");
    int counter = 1;
    element *elem = alist->first;
    while (elem != NULL) {
        printf("Book %d\n", counter);
        printf("\tTitel: %s\n", elem->title);
        printf("\tAuthor: %s\n", elem->author);
        printf("\tYear:  %d\n", elem->year);
        printf("\tISBN:  %lld\n", elem->isbn);
        elem = elem->next;
        counter++;
    }
}

int main(int argc, char** argv) {
    list *alist = construct_list();
    read_list(argc>1?argv[1]:"buecherliste.txt", alist);
    print_list(alist);
    free_list(alist);
    return 0;
}

这就是将要打印的内容，您可以看到标题丢失了，一些信息也被截断了。我确实尝试过 X Code Leaks 工具，但在那里找不到任何有用的东西。我在 read_list 的 while 循环中添加了一个用于调试的 printf 函数，它在那里工作得很好。所以它必须与 insert_at_begin 函数有关。

My Books
================

Book 1
    Titel: 
    Author: Phillip K. Dick
    Year:  1973
    ISBN:  9780547572178
Book 2
    Titel: 
    Author: nner Darkly
    Year:  1949
    ISBN:  9783548267456

更新:这是 read_line 函数:

int read_line(read_line_context *ctx, char **name, char **author, int *year, long long int *isbn) {
    if (ctx->filepointer == NULL){
        perror(ctx->filename);
        exit(1);
    }
    char *name_s;
    char *author_s;
    char *year_s;
    char *isbn_s;
    char *delim = ";";
    ssize_t len;

    if ((len = getline(&(ctx->line), &(ctx->linecapp), ctx->filepointer)) != -1)
    {
        /* remove tailing newline */
        char *pos;
        if ((pos = strchr(ctx->line, '\n')) != NULL)
            *pos = '\0';

        /* read individual fields */
        name_s   = strtok(ctx->line, delim);
            author_s = strtok(NULL, delim);
        year_s   = strtok(NULL, delim);
        isbn_s   = strtok(NULL, delim);
        if(name_s != NULL && author_s != NULL && year_s != NULL  && isbn_s != NULL ) {
            *name   = name_s;
            *author = author_s;
            *year   = atoi(year_s);
            *isbn   = atoll(isbn_s);
            return 0;
        }

    }
    fclose(ctx->filepointer);
    ctx->filepointer = NULL;
    ctx->linecapp = 0;
    if (ctx->line != NULL ) {
        free(ctx->line);
    }
    return -1;
}

Answer 1

在我看来，您似乎还没有为 author 和 title 分配任何内存。

struct _element {
    char title[100];
    char author[100];
     int year;
    long long int isbn;
    element *next;
};

会更好，但会将您的标题/作者字符数限制为 100...

所以你真的应该使用 malloc 或 calloc 来分配你需要的内存 - 我建议上面的代码只是为了让事情在快速和肮脏的基础上工作。 ..