如何在for循环中声明和使用结构数组？

Question

I am working on a native winapi application using cpp and sqlite http://github.com/jacksiro/vsongbook-cpp using the falcon c++ IDE. This is my database:

void CreateDatabase()
{
    sqlite3 * db = NULL;
    int db_qry;
    const char * sqlCreateTables = 
        "CREATE TABLE my_friends(friend_name VARCHAR(20), "
        "friend_job VARCHAR(20), friend_job INTEGER(11));";

    db_qry = sqlite3_open("friends.db", &db);
    db_qry = sqlite3_exec(db, sqlCreateTables, NULL, NULL, NULL);
    sqlite3_close(db);
}

And the database I insert it with this:

void InsertToDatabase()
{
    int db_qry;
    char *error;    
    sqlite3 *db;

    const char *sqlInsert = 
        "INSERT INTO my_friends(friend_name, friend_job, friend_age) "
        "VALUES('Ngunjiri James', 'Teacher', 25);"
        "INSERT INTO my_friends(friend_name, friend_job, friend_age) "
        "VALUES('Wafula Shem', 'Capernter', 30);"
        "INSERT INTO my_friends(friend_name, friend_job, friend_age) "
        "VALUES('Jane Akinyi', 'Nurse', 23);";

     db_qry = sqlite3_open("friends.db", &db);
     db_qry = sqlite3_exec(db, sqlInsert, NULL, NULL, &error);
     sqlite3_close(db);
}  

Now I have a simple listbox in my window where I populate it with values from my sqlite table like this.

inline UINT AddStringList(const HWND hList,const ustring& s)
{
    return static_cast<UINT>(SendMessage(hList,LB_ADDSTRING,0,
                         reinterpret_cast<LPARAM>(s.c_str())));
}

//I call this method in my WM_CREATE in WinMain and it works very well
    void AddFriendListBox(const HWND hList)
    {
        sqlite3 * db = NULL;
        sqlite3_stmt * stmt;
        int i, db_qry;
        const char * tail;
        const char * sqlSelect  = "SELECT * FROM my_friends";

    db_qry = sqlite3_open("friends.db", &db);
    if(sqlite3_prepare(db, sqlSelect, -1, &stmt, &tail) == SQLITE_OK)
    {
        while(sqlite3_step(stmt) != SQLITE_DONE)
        {
            for(i = 0; i < sqlite3_column_count(stmt); i++) {
                const unsigned char * p =  reinterpret_cast<const unsigned char *>
                        (sqlite3_column_text(stmt, 0));
                const char * finaltext = (const char *)p;
                AddStringList(hList,_T(finaltext));
                }
            }
        sqlite3_finalize(stmt);
   }

   sqlite3_close(db);
}

I came across some code http://zetcode.com/gui/winapi/advancedcontrols/ on creating a list box and populating it using a struct :

typedef struct {

    wchar_t name[30]; 
    wchar_t job[20]; 
    int age; 

} Friends; 

Friends friends[] = {

    {L"Lucy", L"waitress", 18}, 
    {L"Thomas", L"programmer", 25}, 
    {L"George", L"police officer", 26}, 
    {L"Michael", L"producer", 38}, 
    {L"Jane", L"steward", 28}, 
}; 

Then using it as below:

case WM_CREATE:

            hwndList = CreateWindowW(WC_LISTBOXW , NULL, WS_CHILD 
                | WS_VISIBLE | LBS_NOTIFY, 10, 10, 150, 120, hwnd, 
                (HMENU) IDC_LIST, NULL, NULL);


            for (int i = 0; i < ARRAYSIZE(friends); i++)  { 
                 SendMessageW(hwndList, LB_ADDSTRING, 0, (LPARAM) friends[i].name);
            } 

            break;

Since I could not understand the ARRAYSIZE used above. I substituted it with an int 5 as below:

case WM_CREATE:

        hwndList = CreateWindowW(WC_LISTBOXW , NULL, WS_CHILD 
            | WS_VISIBLE | LBS_NOTIFY, 10, 10, 150, 120, hwnd, 
            (HMENU) IDC_LIST, NULL, NULL);

        for (int i = 0; i < 5; i++)  { 
             SendMessageW(hwndList, LB_ADDSTRING, 0, (LPARAM) friends[i].name);
        } 

        break;

Okay now that said and done.

How do I create a struct similar to the one above of friends and populate it with values from my sqlite3 table using the for loop ?

I am still a novice in c/c++.

Answer 1

Since I could not uderstand the "ARRAYSIZE" used above I substituted it with an int 5 as below

It's most likely a macro, which can defined as:

#define ARRAYSIZE(array) (sizeof(array)/sizeof(array[0]))

This works fine for arrays that are defined in the same function where the macro is used. It won't work when the array is passed to a function. In a function that get an array as an argument, sizeof(array) will evaluate to the size of a pointer, not the size of the array.

Eg

void foo(int array[])
{
   int s = ARRAYSIZE(array); // Won't work here.
}

void foo()
{
   int array[] = {1, 3, 20};
   int s = ARRAYSIZE(array); // Will work here.
}

If you have the option, you should use std::vector . That will make coding a lot easier in the long run.

In C++11, you can define friends as:

std::vector<Friends> friends = {
    {L"Lucy", L"waitress", 18}, 
    {L"Thomas", L"programmer", 25}, 
    {L"George", L"police officer", 26}, 
    {L"Michael", L"producer", 38}, 
    {L"Jane", L"steward", 28}, 
};