如何从二进制文件中写入和读取动态数组

Question

我有这个结构

    struct _recipe
{
    char name[50];
    char** ingredients;
    char diff[12];
    int time;
    int calories;
    char** procedure;   
} recipe;

我想复制二进制文件中的所有数据。 首先，我已经为成分和程序动态分配了内存，并且我已经编写了我需要的所有内容。但是我需要将所有内容都写在一个二进制文件中。我知道它们都是指针，所以这意味着如果我使用

fwrite(&recipe,sizeof(recipe),1,fbr);

我将在文件中写入地址，而不是我需要的实际值。我已经尝试以这种方式在文件中编写结构的每个字段

    fwrite(recipe.name,sizeof(recipe.name),1,fbr);

    fgets(recipe.ingredients[j],30,stdin);
            strcpy(buff,recipe.ingredients[j]);
            len = strlen(buff);
            fwrite(buff,sizeof(recipe.ingredients[0]),len,fbr);

   fwrite(recipe.diff,sizeof(recipe.diff),1,fbr);
   fwrite(&recipe.time,sizeof(recipe.time),1,fbr);
   fwrite(&recipe.calories,sizeof(recipe.calories),1,fbr);

    fgets(recipe.procedure[i],1000,stdin);
            strcpy(buff,recipe.procedure[i]);
            len = strlen(buff);
            fwrite(buff,sizeof(recipe.procedure[0]),len,fbr);

我不确定这是否正确，但我尝试将字符串放入另一个字符串，然后将其复制到文件中。问题是，我不确定它是否有效，因为我不知道应该使用什么样的命令来读取我存储的所有值。当然，它的名称有效，我对此没有任何问题，但是当我要阅读成分时，我阻止了自己，因为我将值写在另一个字符串中并且我不知道我应该输入什么长度阅读。也许我错过了一些东西，也许我一开始就在写东西，但我现在不知道该怎么办。

Answer 1

你想做这样的事情来写出你的食谱：

    fwrite(recipe.name,sizeof(recipe.name),1,fbr);
    for (int i = 0; i < num_ingredients; i++) {
            int len = strlen(recipe.ingredients[i]) + 1;
            int num_elements = fwrite(recipe.ingredients[i],sizeof(char),len,fbr);
            printf("wrote %d elements for %s\n", num_elements, recipe.ingredients[i]);
    }
    fwrite(recipe.diff,sizeof(recipe.diff),1,fbr);
    for (int i = 0; i < num_procedures; i++) {
            int len = strlen(recipe.procedure[i]) + 1;
            int num_elements = fwrite(recipe.procedure[i],sizeof(char),len,fbr);
            printf("wrote %d elements for %s\n", num_elements, recipe.procedure[i]);
    }

当然，您还需要写出卡路里和时间。在将任何内容读入结构之前，我也会这样做：

memset(&recipe, 0, sizeof(struct _recipe));

如果您使用 fprintf 以 \n 为分隔符写出卡路里和时间，您的食谱文件将如下所示：

$ od -c recipe.bin
0000000   m   u   f   f   i   n   s  \0  \0  \0  \0  \0  \0  \0  \0  \0
0000020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
0000060  \0  \0   f   l   o   u   r  \0   s   u   g   a   r  \0   e   g
0000100   g   s  \0   v   a   n   i   l   l   a  \0   n   u   t   s  \0
0000120   n   o       d   i   f   f  \0  \0  \0  \0  \0   m   i   x  \0
0000140   b   a   k   e  \0   r   e   s   t  \0   6   0  \n   2   5   0
0000160  \n

Answer 2

您可以设计一个简单的存储protocol 用于写入/读取。

例如：

| struct recipe | t l v | t l v | ... | t l v | struct recipe | t l v | ... | t l v |

|<-      a complete struct recipe data      ->|


| description | t(ype) | l(ength) | v(alue)|
| ingredient  | i      | strlen() | string |
| procedure   | p      | strlen() | string |
| data end    | e      | 0        | <null> |

读取配方数据：

1. Read a struct recipe.
2. Read a t, t=='i' -- go (3.), t=='p' -- go (4.), t=='e' -- go (5.).
3. Read a l, then read a string whose length is l as an ingredient. Go (2.).
4. Read a l, then read a string whose length is l as a procedure. Go (2.).
5. Finish.

写入配方数据：

1. Write a struct recipe.
2. Write ingredients to `i strlen(ingredient) ingredient` one by one.
3. Write procedures to `p strlen(procedure) procedure` one by one.
4. Write `e 0`.
5. Finish.

伪代码：（只是一个demo，请自行设计protol-）

void write_recipe(recipe *r, FILE *fp)
{
    fwrite(r, sizeof(recipe), 1, fp);
    // ...
    for ()
    {
        sprintf(buff, "i %5d %s", strlen(r->ingredients[i]), r->ingredients[i]);
        fwrite(buff, strlen(buff), 1, fp);
    }
    sprintf(buff, "e 0");
    fwrite(buff, strlen(buff), 1, fp);
    //...
    for ()
    {
        sprintf(buff, "p %5d %s", strlen(r->procedure[i]), r->procedure[i]);
        fwrite(buff, strlen(buff), 1, fp);
    }
    sprintf(buff, "e 0");
    fwrite(buff, strlen(buff), 1, fp);
    // ...
}

void read_recipe(FILE *r, FILE *fp)
{
    fread(r, sizeof(recipe), 1, fp);
    // ...
    while (true)
    {
        fread(&t, sizeof(char), 1, fp);
        if (t == 'e')
        {
            // ...
            break;
        }
        fread(buff, sizeof(char), 7, fp);
        sscanf("%d", &len);
        fread(buff, sizeof(char), len, fp);
        buff[len] = 0;

        ingredient = malloc(sizeof(char) * (len + 1));
        strcpy(ingredient, buff);
        // ...
    }
    // ...
    while (true)
    {
        fread(&t, sizeof(char), 1, fp);
        if (t == 'e')
        {
            // ...
            break;
        }
        fread(buff, sizeof(char), 7, fp);
        sscanf("%d", &len);
        fread(buff, sizeof(char), len, fp);
        buff[len] = 0;

        procedure = malloc(sizeof(char) * (len + 1));
        strcpy(procedure, buff);
        // ...
    }
    // ...
}