遍历C中未知大小的结构成员的结构数组 [英] Iterate through array of structs with unknown size struct member in C

问题描述

我知道 stackoverflow.com 上有很多类似的问题，但我自己也找不到解决方案.经过一段时间的研究，即使我认为我想做的任务相对简单，我的大脑现在还是受伤了.

I know that there are a many similar questions out there on stackoverflow.com but I couldn't figure out a solution for myself. After quite some time on research, my brain is broken now even though I think the task I want to do is relatively simple.

所以我有两个结构:

struct files_t {
    file_t *file;
};

struct file_t {
    unsigned char *bytes;
    unsigned int len;
};

• 第一个结构 files_t 包含不​​明数量的第二个结构 file_t 的结构.
• 第二个结构 file_t 包含一个 unsigned char 数组，该数组表示 file_t 的字节以及此 bytes的长度 -array.
• The first struct files_t contains a unknown amount of structs of the second struct file_t.
• The second struct file_t contains an array of unsigned char which represents the bytes of the file_t and the length of this bytes-array.

然后我创建一个指向 files_t 结构的指针:

Then I create myself a pointer to a files_t struct:

files_t* files;

我现在的问题是:当文件中的file_t的数量未知时，如何遍历此 files 结构指针(伪代码:对于文件中的每个文件)编译时，每个file_t的大小在编译时都不知道吗?

My question now is: How can I iterate through this files struct pointer (Pseudocode: for each file in files) when the amount of file_t's in it is unknown at compile time and also the size of each file_t is unknown at compile time?

推荐答案

现在我的问题是:(1)当(2)时，如何遍历此文件的结构指针(伪代码:对于文件中的每个文件)其中 file_t 的数量在编译时未知，并且(3)每个 file_t 的大小在未知时编译时间?

My question now is: (1) How can I iterate through this files struct pointer (Pseudocode: for each file in files) when (2) the amount of file_ts in it is unknown at compile time and also (3) the size of each file_t is unknown at compile time?

让我们从语句(3)开始:对您来说，好消息是，每个 file_t 的大小在编译时都是绝对已知的.它是将 * 的大小加到整数的大小上，并且您可以在需要时使用 sizeof(file_t)来获得它.

Let's start from statement (3): the good news, for you, is that the size of each file_t is absolutely known at compile time. It will be the size of a char * added to the size of an integer, and you can obtain that whenever you need it with sizeof(file_t).

这不是一个坏消息:由于语句(2)是真实的(编译时未知其中的 file_t s数量)，不幸的是，对的回答(1)是:您不能.至少，您不能不做任何修改.

Not the bad new: Since statement (2) is true (the amount of file_ts in it is unknown at compile time) unfortunately the answer to (1) is: you can't. At least, you can't without modifying something.

要知道 struct files_t 列表中有多少个项目(有一种迭代方法)，您必须选择:

In order to know how many items there are in your struct files_t list (that is having a way to iterate through it) you have to options:

1. 向 struct files_t 添加一个包含项数的字段:
1. Add a field to struct files_t containing the number of items:

    struct files_t {
        file_t *file;
       unsigned int nrOfFiles;
    };

您将小心地将其初始化为0，每当将文件添加到列表中时将其递增，而从其中删除文件时将其递减.您可以使用诸如 for(int i = 0; i< filesList.nrOfFiles; i ++)之类的for循环遍历它.

You will take care to initialize it to 0, to increment it whenever you add a file to the list and to decrement it whenever you remove a file from it. You can iterate through it with a for loop with something like for(int i=0; i<filesList.nrOfFiles; i++).

1. 设计一个哨兵值.前哨值表示这是数组的最后一个元素".例如:

struct files_t {
    file_t *file;
};

struct file_t {
    unsigned char *bytes;
    unsigned int len;
};

struct file_t fileArray =
{
  { charPointer0, len01 },
  { charPointer1, len1 },
  /* ... */
  { charPointerN, lenN },
  /* Sentinel */
  { NULL, 0 }
};

struct files_t fileList = { fileArray };

在这种情况下，您可以迭代直到找到 {NULL，0} 元素.

In this case you can iterate until the { NULL, 0 } element is found.

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