创建一个char *的2D数组，并使用回调函数中的sqlite数据填充它 [英] Creating an 2D Array of char* an fill it with data from sqlite in callback function

问题描述

在我的函数中，我用callback函数调用rc = sqlite3_exec(db, sqlStatement, callback, &a, &zErrMsg);函数. 在此callback函数中，我想用数据库中的数据填充char *的2D数组.

In my function I call the rc = sqlite3_exec(db, sqlStatement, callback, &a, &zErrMsg); function with the callback function. In this callback function I want to fill a 2D Array of char* with the data from the database.

struct mytable 
{
    char ***data;
    size_t dim;
};

static int callback(void *data, int argc, char **argv, char **azColName)
{
    struct mytable *old = (mytable *)data;
    char ***temp;

    old->dim++;
    temp = (char ***)realloc(old->data, old->dim * sizeof(*old->data));
    if (temp) 
    {
        old->data = temp;
        old->data[old->dim - 1] = NULL;
    }
    else 
    {
        logging_logError("Kein virtueller RAM mehr vorhanden ... !", __FILE__);
        return EXIT_FAILURE;
    }

    for (int i = 0; i < old->dim; i++) 
    {
        char **temp2 = (char **)realloc(old->data[i], sizeof(argv) * sizeof(*old->data[i]));

        if (temp2) 
        {
            old->data[i] = temp2;
            old->data[i][argc - 1] = NULL;
        }
        else 
        {
            logging_logError("Kein virtueller RAM mehr vorhanden ... !", __FILE__);
            return EXIT_FAILURE;
        }
    }

    /*Here I try to store the data from each column 
     in the corresponding position in the 2D array of char* */
    for (int i = 0; i < argc; i++)
    {
        char *s = argv[i];
        temp[old->dim - 1][i] = s;
    }
    return 0;
}

当我打印出我返回的数据时，我得到了一些神秘的迹象. 我想拥有的是这样的东西(在数组结构中):

When I print out the data I returned, I get some mysterious signs. What I want to have is something like this (in array structure):

["1"]["Paul"]["street 1"]["some address"]
["2"]["Anna"]["street asdf"]["some address"]
["3"]["Martin"]["street bfg"]["some address"]

这是我以前的问题

推荐答案

我没有找到专门的文档，但是传递到回调中的argv字符串似乎只有在回调返回之前才有效.我不知道SQLite可以如何工作-回调函数不负责管理这些字符串的内存，因此SQLite必须在内部进行操作.

I don't find it documented specifically, but it seems probable that the argv strings passed into your callback are good only until the callback returns. I don't see how SQLite could work otherwise -- the callback is not responsible for managing the memory for those strings, so SQLite must do so internally.

因此，不要在数组中记录原始的字符串指针，而是复制字符串，并存储指向重复项的指针. MSVC ++提供了strdup()，因此您可以通过替换...

Therefore, instead of recording the original string pointers in your array, duplicate the strings, and store pointers to the duplicates. MSVC++ provides strdup(), so you might achieve that by replacing ...

        char *s = argv[i];

...和...

        char *s = strdup(argv[i]);

.请注意，这样做后，您将承担在处理完这些字符串后将其释放的责任.

. Do be aware that by doing so you assume responsibility for freeing those strings when you're done with them.

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