C++ mysql准备好的语句close和unique_ptr

Question

我有 2 个与 C++ 和 mysql 连接器相关的问题。

1. 如果我使用sql::PreparedStatement作为unique_ptr，是否需要调用prepareStatement的close()方法，还是在删除unique_ptr时自动调用它？我还需要关闭 sql::resultSet 吗？

2. 是否需要调用unique_ptr的reset()方法来删除该指针？

我有这个函数，它从PreparedStatement接收unique_ptr，执行查询并返回结果。

    std::unique_ptr<sql::ResultSet> CommonService::select(std::unique_ptr<sql::PreparedStatement> &pstmt) {
std::unique_ptr<sql::ResultSet> resulSet = nullptr;
    try {
        resulSet = std::unique_ptr<sql::ResultSet>(pstmt->executeQuery());
        pstmt->close(); // i need to do this? or is closed when unique_ptr is deleted?
       // pstmt.reset(); i need to do this? or is deleted automatically
    } catch (sql::SQLException &e) {
        std::cout << "# ERR: SQLException in " << __FILE__;
        std::cout << "(" << __FUNCTION__ << ") on line " << __LINE__ << std::endl;
        std::cout << "# ERR: " << e.what();
        std::cout << " (MySQL error code: " << e.getErrorCode();
        std::cout << ", SQLState: " << e.getSQLState() << " )" << std::endl;
        pstmt->close(); // i need to do this? or is closed when unique_ptr is deleted?
    }

    return resulSet;
}

谢谢

Answer 1

If I use sql::PreparedStatement as unique_ptr, do I need to call the close() method of prepareStatement or is it called automatically when unique_ptr is deleted? Do I also need to close the sql::resultSet?

不，您不需要调用 close() 方法。像这样只初始化一次查询语句。一旦超出范围，查询语句将被自动销毁。处理数据库异常而不关闭语句。

就您的 resultSet 而言，您可以将其声明为局部变量，如下所示

// global scope
std::unique_ptr<sql::Connection> sqlConnection;
std::unique_ptr<sql::Statement> stmt;

void InitializeDatabase() { // call once
   sqlConnection.reset(sqlDriver->connect(host, user, pwd));
   stmt.reset(sqlConnection->createStatement());
}

void getData(/* */)
{    
    std::unique_ptr<sql::ResultSet> res(stmt->executeQuery(/**/));    
    do {
        while (res->next()) {  // extract data from statement
            /* */
        }
    } while (stmt->getMoreResults());  
} // res will be automatically destroyed here.

Do you need to call the reset () method of unique_ptr to remove that pointer?

不，unique_ptr 对象一旦超出范围就会自动销毁。