[英]Using SQLite in C++: object function as a callback
So, I am working on a side-project to keep my c++ skills fresh (it has been many years since I have done work in c++). 因此,我正在开展一个侧面项目,以保持我的c ++技能新鲜(自从我用c ++完成工作已经很多年了)。 I am working on something where I will be using SQLite.
我正在开发一些我将使用SQLite的东西。 I have a wrapper around the SQLite code.
我有一个SQLite代码的包装器。 One of the things I am noticing is that SQLite uses c-style callback functions in its sqlite3_exec(...) function.
我注意到的一件事是SQLite在其sqlite3_exec(...)函数中使用了c风格的回调函数。
I would like to have the callback function be an object method, as I would like it to be able to modify object variables but am unsure of how to do this exactly. 我想让回调函数成为一个对象方法,因为我希望它能够修改对象变量,但我不确定如何准确地执行此操作。 I have checked other similar questions on stackoverflow but came away with nothing helpful.
我已经检查了stackoverflow上的其他类似问题,但没有任何帮助。
Here is how I am declaring my wrapper class: 这是我如何声明我的包装类:
class DBAdapter
{
private:
sqlite3* db;
int getUserRecords(std::string);
std::vector<USER_RECORD> records;
int callbackSel(void*, int , char**, char**);
public:
DBAdapter();
~DBAdapter();
int open(std::string);
void close();
int insertRecord();
int deleteRecord();
int getNumUserRecords();
};
Here is how I am trying to use the callback (callbackSel), from within getNumUserRecords: 以下是我在getNumUserRecords中尝试使用回调(callbackSel)的方法:
int DBAdapter::getUserRecords(std::string name)
{
std::string sql = "SELECT" + name + " from USERS";
char* ErrMsg;
char* data;
int retval = sqlite3_exec(db,sql.c_str(),this->callbackSel,data,&ErrMsg);
return retval;
}
The error message I am getting is: 我得到的错误消息是:
error: ‘int (* DBAdapter::callbackSel)(void*, int, char**, char**)’ is not a static member of ‘class DBAdapter’
My problem is, if I make this a static function, I won't be able to have access to my vector, records, right? 我的问题是,如果我将其设为静态函数,我将无法访问我的向量,记录,对吧? Is there any way around this?
有没有办法解决?
Is there any way around this?
有没有办法解决?
I don't know for sqlite API specifically, but usually c-style callbacks support to have user data passed from a void*
pointer (I'd guess the 1st parameter of that signature you mention). 我不知道sqlite API具体,但通常c风格的回调支持从
void*
指针传递用户数据(我猜你提到的那个签名的第一个参数)。 What one typically does is: 通常做的是:
I hope this points out the right direction. 我希望这指出了正确的方向。
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