PHP 字符串

$str1 = "Hello, world!";   // 双引号字符串
$str2 = 'Hello, world!';   // 单引号字符串

$str1 = "Hello";
$str2 = "world";
$str3 = $str1 . ", " . $str2 . "!";   // 将三个字符串连接在一起
echo $str3;   // 输出：Hello, world!

$str = "Hello";
$str .= ", world!";   // 追加字符串
echo $str;   // 输出：Hello, world!

$words = array("Hello", "world", "!");
$str = implode(", ", $words);   // 连接数组元素为一个字符串
echo $str;   // 输出：Hello, world!

$str = "Hello, world!";
$length = strlen($str);
echo $length;   // 输出：13

$str = "Hello, world!";
$substring = substr($str, 0, 5);   // 从索引位置0开始截取5个字符
echo $substring;   // 输出：Hello

$str = "Hello, world!";
$substring = strstr($str, "world");
echo $substring;   // 输出：world!

$str = "Hello, world!";
$newStr = str_replace("world", "everyone", $str);
echo $newStr;   // 输出：Hello, everyone!

$str = "Hello, World!";
$lowercase = strtolower($str);   // 转换为小写字母
$uppercase = strtoupper($str);   // 转换为大写字母
echo $lowercase;   // 输出：hello, world!
echo $uppercase;   // 输出：HELLO, WORLD!

$str1 = "Hello";
$str2 = "hello";
$result = strcmp($str1, $str2);
if ($result === 0) {
    echo "两个字符串相等";
} elseif ($result < 0) {
    echo "字符串1小于字符串2";
} else {
    echo "字符串1大于字符串2";
}

$str = "Hello, world!";
$chars = str_split($str);
print_r($chars);   // 输出：Array ( [0] => H [1] => e [2] => l [3] => l [4] => o [5] => , [6] =>   [7] => w [8] => o [9] => r [10] => l [11] => d [12] => ! )

$name = "John";
$age = 30;
$str = sprintf("My name is %s and I am %d years old.", $name, $age);
echo $str;   // 输出：My name is John and I am 30 years old.

$str = "Hello, world!";
$reversedStr = strrev($str);
echo $reversedStr;   // 输出：!dlrow ,olleH

$str = "password";
$hashedStr = md5($str);   // 使用 md5 算法进行哈希加密
echo $hashedStr;   // 输出：5f4dcc3b5aa765d61d8327deb882cf99

$password = "password";
$hashedPassword = password_hash($password, PASSWORD_DEFAULT);   // 使用默认算法进行哈希加密
echo $hashedPassword;   // 输出：$2y$10$pOZL0zqNVCJKxrw6KC.G3.IKzbzyrAGAulqMjewI2X2Q7ME.FYKDq

$str = "apple,banana,cherry";
$fruits = explode(",", $str);
print_r($fruits);   // 输出：Array ( [0] => apple [1] => banana [2] => cherry )

$str = "  Hello, world!  ";
$trimmedStr = trim($str);
echo $trimmedStr;   // 输出：Hello, world!

$str = "123456";
if (preg_match("/^\d{6}$/", $str)) {
    echo "字符串是一个6位数字";
} else {
    echo "字符串不是一个6位数字";
}

$str = "Hello, world!";
$repeatedStr = str_repeat($str, 3);
echo $repeatedStr;   // 输出：Hello, world!Hello, world!Hello, world!