ANSI C 和 sqlite3_get_table：如何将结果数组传递回调用 function？

Question

I'm trying to pass the results array generated by sqlite3_get_table contained in a function called by another function. Everything is working fine except I can't get the array back into the main function. What exactly do I replace the char **sql_results with? Here's the code:

int main()
{
    char **sql_results = 0; // help here

    sql_select_table("GetAirports", query_string, AIRPORTS_DATABASE,
             sql_results, &RecordCount,
             &ColumnCount);

    for (int i = 0; i < ColumnCount; i++)
        printf("%s\n", sql_results[i]); // Generates "EXC_BAD_ACCESS"

}

void sql_select_table(const char *query_name, const char *sql_query,
              const char *sql_database,
              char **sql_results, int *RecordCount,
              int *ColumnCount)
{
    sqlite3_get_table(open_database, sql_query,
                 &sql_results, RecordCount,
                 ColumnCount, &error_msg);

}

Answer 1

You're trying to take the address of one of the sql_select_table arguments and that doesn't do what you think it does; &sql_results is just the address of a local variable, it won't let you modify the sql_results in main() .

Instead, pass a char*** into sql_select_table like this:

/* Note that sql_results is now a char*** */
void sql_select_table(const char *query_name, const char *sql_query,
              const char *sql_database,
              char ***sql_results, int *RecordCount,
              int *ColumnCount)
{
    sqlite3_get_table(open_database, sql_query,
                 sql_results, RecordCount,
                 ColumnCount, &error_msg);

}

int main()
{
    char **sql_results = 0;

    /* Note the & on sql_results */
    sql_select_table("GetAirports", query_string, AIRPORTS_DATABASE,
             &sql_results, &RecordCount,
             &ColumnCount);

    for (int i = 0; i < ColumnCount; i++)
        printf("%s\n", sql_results[i]); // Generates "EXC_BAD_ACCESS"

}

Also, sqlite3_get_table is deprecated:

This is a legacy interface that is preserved for backwards compatibility. Use of this interface is not recommended.

So you might want to start using sqlite3_exec instead.