我想將 a 傳遞std::list給我的回呼函式。我知道我必須void*在回呼函式中使用，但是在使用時如何將物件插入到我的串列中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);
}
我嘗試將void*回呼函式中的 in 更改為std::list<Album>并希望sqlite3_exec()使用該回呼函式。
uj5u.com熱心網友回復：
您已經知道如何將 a強制list*轉換為 a void*（順便說一句，顯式強制轉換是多余的）。只需在回呼中進行相反的轉換，例如：
int callbackAlbums(void* data, int argc, char** argv, char** azColName)
{
Album album;
...
std::list<Album>* albums = (std::list<Album>*)data;
albums->push_back(album);
...
}
并且不要忘記實際上是return您的std::listfrom getAlbums()：
const std::list<album> DatabaseAccess::getAlbums()
{
std::list<Album> albums;
...
int res = sqlite3_exec(..., callbackAlbums, &albums, ...);
...
return albums;
}
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