PHP 笔记(一)
数据库项目作业要团队开发 web，选择了尝试后端，又向做出自己的网站这个目标踏出了一步。
1. 简单使用
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| <!DOCTYPE html>
<html>
<body>
<h1>h1</h1>
<?php
echo "Hello World!";
?>
<h1>h1</h1>
</body>
</html>
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在服务器下运行才有效果
2. 变量
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| <?php
$x = 1;
$y = 1;
$z = $x + $y;
echo $z;
?>
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2.1 变量作用域
PHP 有四种作用域
- local
- global
- static
- parameter
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| <?php
$x = 5;
function fn()
{
$y = 10;
echo "<p>函数内: </p>";
echo "<br>";
echo "变量y: $y";
}
fn();
echo "<p>函数外: </p>";
echo "变量x: $x";
?>
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global 关键字：
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| <?php
$x = 1;
$y = 1;
function test()
{
global $x, $y;
$y = $x + $y;
}
test();
echo "变量y: $y";
?>
<?php
$x = 1;
$y = 2;
function test()
{
$GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}
test();
echo "变量y: $y";
?>
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static 关键字：
当一个函数完成时，它的所有变量通常都会被删除，在第一次声明变量时使用static 关键字可以实现让特定变量不被删除。然后，每次调用该函数时，该变量都会保留函数前一次被调用时的值。该变量还是函数的局部变量
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| <?php
function test() {
static $x = 0;
echo $x;
$x++;
echo "<br>";
}
test();
test();
test();
?>
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3. 定界符 EOF
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<?php
$name = "clz";
echo <<<EOF
<h1>测试</h1> // html格式会被解析
"abg\n"$name // 双引号也会被解析，双引号内会保留转义符的转义效果
"123"
EOF;
echo "Hello World!";
?>
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4. 数据类型
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| <?php
$x = 123;
var_dump($x);
$x = -234;
var_dump($x);
$x = 017;
var_dump($x);
$x = 0xaa;
var_dump($x);
$x = "test";
var_dump($x);
$x = 1.234;
var_dump($x);
$x = 2.4e3;
var_dump($x);
$x = true;
var_dump($x);
?>
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| <?php
$arr = array(1, "Hello", true);
var_dump($arr);
var_dump($arr[0]);
class Car
{
var $color;
function __construct($color="green") {
$this->color = $color;
}
function what_color() {
return $this->color;
}
}
$c = new Car("white");
var_dump($c);
$d = null;
var_dump($d);
?>
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5. 类型比较
和 JavaScript 一样，有松散比较和严格比较两种形式
- 松散比较(等于)：”==”, 只比较值，不比较类型
- 严格比较(绝对等于)：”===”, 既比较值，也比较类型
6. 常量
设置常量需要使用 define()函数
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| bool define ( string $name , mixed $value [, bool $case_insensitive = false ] )
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- name: 必选参数，常量名称
- value: 必选参数，常量的值
- case_insensitive: 可选参数，如果是 true，则常量对大小写不敏感。默认是大小写敏感。
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| <?php
define("HW", "Hello World!");
echo HW;
echo "<br>";
function test() {
echo HW;
}
test();
?>
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7. 字符串
7.1 并置运算符(.)
用于把两个字符串连接起来
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| <?php
$h = "Hello ";
$w = "World";
echo $h . $w;
?>
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7.2 strlen()函数
strlen()函数返回字符串的长度(字节数), echo strlen("中文");会输出 6，因为一个中文占 3 个字节
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| <?php
$h = "Hello ";
$w = "World";
echo strlen($h . $w);
?>
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7.3 strpos()函数
strpos()函数用于在字符串中查找字符串，如果找到匹配，则返回第一个匹配的字符位置，如果找不到，则返回 false
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| <?php
echo strpos("Hello World!", "!");
echo "<br>";
echo strpos("Hello World!", "World");
echo "<br>";
var_dump(strpos("Hello World!", "Worll"));
?>
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8. 关联数组
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| <?php
$age = array("A" => 17, "B" => 33, "C" => 21);
echo "A is " . $age['A'] . " years old.";
echo "<br>";
foreach($age as $k => $v)
{
echo "Key = " . $k . ", Value = " .$v;
echo "<br>";
}
?>
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9. 支持可变参数的函数
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| <?php
echo "<pre>";
function test(...$args)
{
$num = count($args);
echo "函数调用参数个数: " . $num . PHP_EOL;
echo "函数参数详情: ";
foreach($args as $args)
{
echo $args . " ";
}
echo PHP_EOL;
}
test("a");
test("a", "b");
test("a", "b", "c");
?>
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10. 数据库
10.1 连接数据库
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| <?php
$servername = "localhost";
$username = "root";
$password = "密码";
$conn = new mysqli($servername, $username, $password);
if($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
echo "连接成功";
$conn->close();
?>
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
$conn = mysqli_connect($servername, $username, $password);
if(!$conn) {
die("连接失败: " . mysqli_connect_error());
}
echo "连接成功";
mysqli_close($conn);
?>
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
try
{
$conn = new PDO("mysql:host=$servername;", $username, $password);
echo "连接成功";
}
catch(PDOException $e)
{
echo $e->getMessage();
}
$conn = null;
?>
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10.2 创建数据库
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
$conn = new mysqli($servername, $username, $password);
if($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
$sql = "create database php_db";
if($conn->query($sql) === true) {
echo "数据库创建成功";
} else {
echo "数据库创建失败: " . $conn->error;
}
$conn->close();
?>
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
$conn = mysqli_connect($servername, $username, $password);
if(!$conn) {
die("连接失败: " . mysqli_connect_error());
}
$sql = "create database php_db_1";
if(mysqli_query($conn, $sql)) {
echo "数据库创建成功";
} else {
echo "数据库创建失败: " . mysqli_error($conn);
}
mysqli_close($conn);
?>
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
try {
$conn = new PDO("mysql:host=$servername", $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$sql = "create database php_db_2";
$conn->exec($sql);
echo "数据库创建成功";
}
catch(PDOException $e)
{
echo $sql . " " . $e->getMessage();
}
$conn = null;
?>
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10.3 创建表
MySQLi 面向对象
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| <?php
$servername = "localhost";
$username = "root";
$password = "root1234";
$dbname = "php_db";
$conn = new mysqli($servername, $username, $password, $dbname);
if($conn->connect_error) {
die("连接失败: " . $conn->connect_error);
}
$sql = "create table guests_1(
id int(6) unsigned auto_increment primary key,
firname varchar(30) not null,
lastname varchar(30) not null,
email varchar(50),
reg_date timestamp
)";
if($conn->query($sql) === true) {
echo "创建表成功";
} else {
echo "创建表失败: " . $conn->error;
}
$conn->close();
?>
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其他操作，基本类似，具体实现可查PHP 教程 | 菜鸟教程 (runoob.com)
参考：PHP 教程 | 菜鸟教程 (runoob.com)
