c++ - 如何使用C++在sqlite3数据库中执行writefile函数

Question

我正在尝试使用C++函数从sqlite3数据库中转储文件。
我已经在终端命令上尝试过了，它可以正常工作，但是这里没有执行。

errmsg =:
没有这样的功能:writefile

bool Database::download(string username, string filename){

    string query = "SELECT USERNAME FROM FILES WHERE USERNAME='"+username+"';";
    int rc = sqlite3_exec(dbFile,query.c_str(),private_callback,(void *)data,&errmsg);
    if(rc==SQLITE_OK){
        cout<<"this username dont have any uploaded files!"<<endl;
        return false;

    }
    else{
        query = "SELECT writefile('"+filename+"',FILE) FROM FILES WHERE USERNAME='"+username+"' AND FILENAME='"+filename+"';";
        rc = sqlite3_exec(dbFile,query.c_str(),private_callback,(void *)data,&errmsg);

        if(rc!=SQLITE_OK){
            cout<<errmsg<<endl;
            return false;
        }
        elsereturn true;
    }
}

Answer 1

documentation说:

Note that the readfile(X) and writefile(X,Y) functions are extension functions and are not built into the core SQLite library. These routines are available as a loadable extension in the ext/misc/fileio.c source file in the SQLite source code repositories.