How to work with the 4th argument of the sqlite3

I want to pass a std::list to my callback function. I understand that I have to work with void* in my callback function, but how exactly do I insert objects to my list while working with void*?

//function will insert to a list of albums (data) a new album
int callbackAlbums(void* data, int argc, char** argv, char** azColName)
{
    Album album;
    
    for(int i = 0; i < argc; i  )
    {
        if (std::string(azColName[i])) == "NAME")
        {
            album.setName(std::string(argv[i]));
        }
        else if (std::string(azColName[i])) == "CREATION_DATE")
        {
            album.setCreationDate(std::string(argv[i]));
        }
        else if (std::string(azColName[i])) == "USER_ID")
        {
            album.setOwner(atoi(argv[i]));
        }
    }
    
    data.push_back(album);
    return 0;
}

//function will return a list of all albums.
const std::list<album> DatabaseAccess::getAlbums()
{
    const char* sqlStatement = "SELECT * FROM ALBUMS;";
    std::list<Album> albums;
    char* errMessage = "";
    int res = sqlite3_exec(this->_db, sqlStatement, callbackAlbums, (void*)&albums, &errMessage);
}

I tried changing the void* in my callback function to std::list<Album> and expected sqlite3_exec() to work with that callback function.

CodePudding user response：

You already know how to cast a list* to a void* (which BTW, that explicit cast is redundant). Simply do the opposite cast inside the callback, eg:

int callbackAlbums(void* data, int argc, char** argv, char** azColName)
{
    Album album;
    ...
    std::list<Album>* albums = (std::list<Album>*)data;
    albums->push_back(album);
    ...
}

And don't forget to actually return your std::list from getAlbums():

const std::list<album> DatabaseAccess::getAlbums()
{
    std::list<Album> albums;
    ...
    int res = sqlite3_exec(..., callbackAlbums, &albums, ...);
    ...
    return albums;
}