C/C++ call by value, call by address, call by reference

標頭都加上
#include <iostream>
using namespace std;
然後使用dev c++

==============================================

int main()
{
  int i=1;
  cout<< i <<endl;  // print 1
}

==============================================

int main()
{
  int i=1;
  cout<< &i <<endl; // print i address
}

==============================================

int main()
{
  int i=1;
  int &j=i;  //讓j的位址指向i的位址(兩個位址會一樣)
  cout<< j << endl; //print j values (That is i values)
  cout<< &j << endl;  // print j address (That is i address)
}

==============================================

int main()
{
  int i=1;
  int *k=&i; //讓k的變數參照i的位址(兩個位址會不一樣)
  cout << k << endl;  // print k values => i address (所以k變數數值列印出來是i的位址）
  cout << &k << endl; // print k address (是指k的位址，不關變數i的事情)
  cout << *k << endl; // print i address pointer values (指的是，k指標變數所參照i位址的數值)
}

=============================================

eclipse java project 應用於XAMPP MySQL

因為我是第一次用jdbc，所以就在這記錄一些事情


首先下載mysql-connector-java-XXXX-bin.jar

download link:http://dev.mysql.com/downloads/connector/j/


然後add external jars，把jar檔放入

之後試著寫一段程式連接

	private Connection conn=null; //Database variable
	public void PracticeDB()
	{
	try
	{
	Class.forName("com.mysql.jdbc.Driver");
	//register driver
	conn=DriverManager.getConnection("jdbc:mysql://120.127.14.91:3306/test","root","110432008");
	}catch(ClassNotFoundException e)
	{
	System.out.println("ClassNotFoundException:"+e.toString());
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	System.out.println("SQLException:"+e.toString());
	}
	}

view raw practiceDB hosted with ❤ by GitHub

會發現出現一個錯誤
ClassNotFoundException:java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

是因為MYSQL 預設是不允許通過遠端存取資料庫

所以必須在mysql command下指令：

1.改表

use mysql;
select user,host,password from user;

update user set host='%' where user='root';

2.授權法

grant all privileges on *.* to 'myuser'@'%' identified by 'mypassword' with grant option;

或者是特定主機才可以連線

grant all privileges on *.* to 'myuser'@'192.168.1.3' identified by 'mypassword' with grant option;

然後重開mysql，之後就能成功存取了


再來下面是實作結果

	package PracticeDB;
	import java.sql.*;
	public class PracticeDB {
	private Connection conn=null; //Database variable
	private Statement stat=null;
	private ResultSet rs=null;
	private PreparedStatement pst=null;
	private String dropDbSQL="Drop table User ";
	private String createDbSQL="Create table User ( "+ "id Integer" + ", name Varchar(20) "+", passwd Varchar(20))";
	//ifNULL 代表如果不是null時跑Ａ，否則是
	private String insertDbSQL="insert into User(id,name,passwd) "+"select ifNULL(max(id),0)+1,?,? From User";
	private String selectDbSQL="select * from User";
	public PracticeDB()
	{
	try
	{
	Class.forName("com.mysql.jdbc.Driver");
	//register driver
	conn=DriverManager.getConnection("jdbc:mysql://120.127.14.91:3306/test","root","110432008");
	}catch(ClassNotFoundException e)
	{
	System.out.println("ClassNotFoundException:"+e.toString());
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	System.out.println("SQLException:"+e.toString());
	}
	}
	public void creatTable()
	{
	try
	{
	stat=conn.createStatement();
	stat.executeUpdate(createDbSQL);
	}catch(SQLException e)
	{
	System.out.println("create DB SQLException:"+e.toString());
	}
	finally
	{
	close();
	}
	}
	private void insertTable(String name, String passwd)
	{
	try {
	pst=conn.prepareStatement(insertDbSQL);
	pst.setString(1, name);
	pst.setString(2, passwd);
	pst.executeUpdate();
	} catch (SQLException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
	}
	finally
	{
	close();
	}
	}
	public void selectTable()
	{
	try
	{
	stat=conn.createStatement();
	rs=stat.executeQuery(selectDbSQL);
	System.out.println("ID\t\tName\t\tPAAWORD");
	while(rs.next())
	{
	System.out.println(rs.getInt("id")+"\t\t"+rs.getString("name")+"\t\t"+rs.getString("passwd"));
	}
	}catch(SQLException e)
	{
	System.out.println("select table SQLException:"+e.toString());
	}
	finally
	{
	close();
	}
	}
	public void dropTable()
	{
	try
	{
	stat=conn.createStatement();
	stat.executeUpdate(dropDbSQL);
	}catch(SQLException e)
	{
	System.out.println("drop table SQLException:"+e.toString());
	}
	}
	public void close()
	{
	try
	{
	if(rs!=null)
	{
	rs.close();
	rs=null;
	}
	if(stat!=null)
	{
	stat.close();
	stat=null;
	}
	if(pst!=null)
	{
	pst.close();
	pst=null;
	}
	}catch(SQLException e)
	{
	System.out.println("close SQLException:"+e.toString());
	}
	}
	public static void main(String args[])
	{
	PracticeDB paracticeDB=new PracticeDB();
	paracticeDB.dropTable();
	paracticeDB.creatTable();
	paracticeDB.insertTable("mark","1234");
	paracticeDB.selectTable();
	}
	}

view raw gistfile1.txt hosted with ❤ by GitHub

reference:
https://blog.yslifes.com/archives/918
https://my.oschina.net/weiweiblog/blog/664373