Fatal error: Class 'LearningPHP1\mysqli' not found

在php文件的头部使用了namespace 结果报错mysqli不在LearningPHP1中,

结论：如果定义了命名空间，在使用mysqli做连接的时候就要指明mysqli所在的命名空间。

<?php
	//localhost/app/php/index.php
	echo "IE快捷键 Ctrl+Tab下一标签页 Ctrl+Shift+Tab前一标签页<br/>";

	// 1.变量的声明
	echo "<h2>1.变量的声明</h2>";
	//$x=5; $y=6; $z=$x+$y; echo $z;

	//2.变量作用域
	echo "<h2>2.变量作用域</h2>";
	$x2= 5;
	function myTest()
	{
		//访问全局变量$x需要加上global关键字
		//也可以这样访问$x : $GLOBALS['x']
		global $x2;
		$y=10;
		echo "<p>测试函数内变量</p>";
		echo "变量x2为:$x2";
		echo "<br/>";
		echo "变量y为:$y<br/>";
	}
	myTest();
	//3.当一个函数运行结束时，内部变量都会被删除，通过static关键字可以不删除
	echo "<h2>3.static关键字</h2>";
	function test2()
	{
		static $x1 = 0;
		echo "static x1: $x1<br/>";
		$x1++;

	}
	test2();
	test2();
	test2();

	//4.参数传递
	echo "<h2>4.参数传递</h2>";
	$x41 = "郑文强";
	function myTest3($x41)
	{
		echo "传入的是:$x41".'<br/>';
		echo '函数名为:'. __FUNCTION__ ;
	}
	myTest3($x41);

	//5. echo/print
	echo "<h2>5.echo/print</h2>";
	/*
		echo - 可以输出一个或多个字符串
		print - 只允许输出一个字符串，返回值总为 1
		echo 是一个语言结构，使用的时候可以不用加括号，也可以加上括号：echo 或 echo()。

	*/
	echo "I'm about to learn PHP!<br/>";
	echo "This ","String ","was ","made ","with multiple parameters.<br/>";

	$txt1="Learn PHP";
	$txt2="w3cschool.cc";
	$cars=array("Volvso","BMW","Toyota");

	echo $txt1,"<br/>";
	echo "Study PHP at $txt2<br/>";
	echo "My car is a $cars[0]";

	//6.数据类型

		echo "<h3>6.数据类型--整型</h3>";
		$x61 = 5985;
		var_dump($x61);
		echo "<br>";
		$x62 = -345; // 负数
		var_dump($x62);
		echo "<br>";
		$x63 = 0x8C; // 十六进制数
		var_dump($x63);
		echo "<br>";
		$x64 = 047; // 八进制数
		var_dump($x64);

		echo "<h3>数据类型--浮点型</h3>";
		$x65= 10.365;
		var_dump($x65);
		echo "<br>";
		$x66 = 2.4e3;
		var_dump($x66);
		echo "<br>";
		$x67 = 8E-5;
		var_dump($x67);

		echo "<h3>数据类型--数组</h3>";
		$cars=array("Volvo","BMW","Toyota");
		var_dump($cars);

		echo "<h3>数据类型--对象</h3>";
		class House
		{
			var $color;
			function House($color="green"){
				$this->color = $color;
			}
			function what_color(){
				return $this->color;
			}
		}

		echo "<h3>数据类型--常量 ,第三个参数默认为false,即区分大小写,这里设为true 不区分大小写</h3>";
		define("GREETING","欢迎访问 xxoo.com",true);
		echo GREETING,"<br/>";
		echo greeting;

	//7.字符串
	echo "<h2>7.字符串 并置运算符</h2>";
		$txt71="Hello Beijing ";
		$txt72="What A Nice Day";
		$txt73 = $txt71.$txt72;
		echo $txt73;
		/*
			strlen($txt73); 字符串长度
			strpos()		函数用于在字符串内查找一个字符或一段指定的文本。如果在字符串中找到匹配，
							该函数会返回第一个匹配的字符位置。如果未找到匹配，则返回 FALSE

		*/
	//8.运算符
	echo "<h2>8.运算符</h2>";
		echo "<h3>取模运算符</h3>";
		$x81=10; $y81=6;
		echo ( $x81 % $y81 );
		echo "<h3>三元运算符</h3>";
		$test81 = '菜鸟教程';
		$username = isset($test81)?$test81:'nobody';
		echo $username,PHP_EOL;
	//9.判断IF语句
		echo "<h2>9.判断IF语句</h2>";
			//判断当前时刻
			$h91=date("H");
			if($h91<16){
				echo "Have A Good Day!";
			}else{
				echo "Have A Good Night!";
			}
	//10.Switch 语句
		echo "<h2>10.Switch语句</h2>";
		$favcolor10="blue";
		switch ($favcolor10)
		{
			case "red":
				echo "你喜欢的颜色是红色!";
				break;
			case "blue":
				echo "你喜欢的颜色是蓝色!";
				break;
			case "green":
				echo "你喜欢的颜色是绿色!";
				break;
			default:
				echo "你喜欢的颜色不是 红, 蓝, 或绿色!";
		}
	//11.数组
		echo "<h2>11.数组</h2>";
		$cars11=array("Volvo","BMW","Toyota");
		echo "I like " . $cars11[0] . ", " . $cars11[1] . " and " . $cars11[2] . ".<br/>";
		$arrlength=count($cars11);
		for($x=0;$x<$arrlength;$x++)
		{
			echo $cars[$x];
			echo "<br>";

		}
		$age11=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
		echo "Peter is " . $age11['Peter'] . " years old.";
		//遍历关联数组
		foreach($age11 as $x=>$x_value)
		{
			echo "Key=" . $x . ", Value=" . $x_value;
			echo "<br>";
		}
	//12.魔术常量
		echo '该文件位于 " '  . __FILE__ . ' "<br/>';
		echo '这是第"'. __LINE__ .'"行<br/>';
		//除非是根目录 否则不能包括末尾的斜杠
		echo '该文件位于"'. __DIR__ .'"';
		echo '命名空间为："', __NAMESPACE__, '"'; // 输出 "MyProject"
	//13.连接数据库
		echo "<h2>连接数据库</h2>";
		$servername = "www.qyying.cn";
		$username = "blog";
		$password = "123";
		$dbname = "myblog";
		//13.1 面向对象创建连接
		$conn0 = new mysqli($servername, $username, $password,$dbname);
		// 检测连接
		if ($conn0->connect_error) {
		die("连接失败: " . $conn0->connect_error);
		}
		echo "面向对象连接成功<br/>";

		//13.2 面向过程创建连接
		$conn1 = mysqli_connect($servername, $username, $password);
		// 检测连接
		if (!$conn1) {
		die("Connection failed: " . mysqli_connect_error());
		}
		mysqli_close($conn1);
		echo "面向过程连接成功<br/>";

		//13.3 PDO创建连接
		try {
			$conn2 = new PDO("mysql:host=$servername;dbname=myblog", $username, $password);
			$conn2=null;
			echo "PDO连接成功";
		}
		catch(PDOException $e)
		{
			echo "出错啦".$e->getMessage()."<br/>";
		}

	//14.创建数据表
		//使用 sql 创建数据表
		$sql = "CREATE TABLE MyGuests (
			id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
			firstname VARCHAR(30) NOT NULL,
			lastname VARCHAR(30) NOT NULL,
			email VARCHAR(50),
			reg_date TIMESTAMP
			)";
		if ($conn0->query($sql) === TRUE)
		{
			echo "Table MyGuests created successfully";
		}else
		{
			echo "创建数据表错误: " . $conn0->error;
		}

		/*
		//插入一条记录
		$sql = "INSERT INTO MyGuests (firstname, lastname, email)
		VALUES ('John', 'Doe', 'john@example.com')";

		if ($conn0->query($sql) === TRUE) {
			echo "新记录插入成功";
		} else {
			echo "Error: " . $sql . "<br>" . $conn0->error;
		}
		//插入多条记录
		$sql = "INSERT INTO MyGuests (firstname, lastname, email)
			VALUES ('John', 'Doe', 'john@example.com');";
		$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
			VALUES ('Mary', 'Moe', 'mary@example.com');";
		$sql .= "INSERT INTO MyGuests (firstname, lastname, email)
			VALUES ('Julie', 'Dooley', 'julie@example.com')";

		if ($conn0->multi_query($sql) === TRUE) {
			echo "新记录插入成功";
		} else {
			echo "Error: " . $sql . "<br>" . $conn->error;
		}

		*/

		$sql = "SELECT id, firstname, lastname FROM MyGuests";
		$result = $conn0->query($sql);
		if ($result->num_rows > 0) {
			// 输出每行数据
			while($row = $result->fetch_assoc())
			{
				echo "<br> id: ". $row["id"]. " - Name: ". $row["firstname"]. " " . $row["lastname"];
			}
		}
		else
		{
			echo "0 个结果";
		}

		$conn0->close();

 ?>