From ffa330cce60b410f9db085579596ffbe28b26e71 Mon Sep 17 00:00:00 2001
From: pengshiyu <1940607002@qq.com>
Date: Mon, 7 Mar 2022 22:55:04 +0800
Subject: [PATCH] fix

---
 blog/php-basic/error.md    |   1 -
 blog/php-basic/function.md |   2 -
 blog/php-basic/index.md    |   2 +
 blog/php-basic/string.md   | 165 +++++++++++++++++++++++++++++++++++++
 4 files changed, 167 insertions(+), 3 deletions(-)
 create mode 100644 blog/php-basic/string.md

diff --git a/blog/php-basic/error.md b/blog/php-basic/error.md
index df03ca3..760086f 100644
--- a/blog/php-basic/error.md
+++ b/blog/php-basic/error.md
@@ -184,4 +184,3 @@ echo $a;
 // NOTICE
 
 ```
-https://www.bilibili.com/video/BV18x411H7qD?p=76&spm_id_from=pageDriver
\ No newline at end of file
diff --git a/blog/php-basic/function.md b/blog/php-basic/function.md
index 6c81314..0bba9bd 100644
--- a/blog/php-basic/function.md
+++ b/blog/php-basic/function.md
@@ -400,5 +400,3 @@ PHP 中实际上不存在的类型
 
 - Mixed： 混合型，可以是多种 PHP 的数据类型
 - Number: 数值型，可以是任意数值类型（整型和浮点型）
-
-https://www.bilibili.com/video/BV18x411H7qD?p=70&spm_id_from=pageDriver
diff --git a/blog/php-basic/index.md b/blog/php-basic/index.md
index 9f1a2d1..cd5e232 100644
--- a/blog/php-basic/index.md
+++ b/blog/php-basic/index.md
@@ -21,3 +21,5 @@
 [PHP 函数 function](blog/php-basic/function.md)
 
 [PHP 错误处理 error](blog/php-basic/error.md)
+
+[PHP 字符串 String](blog/php-basic/string.md)
diff --git a/blog/php-basic/string.md b/blog/php-basic/string.md
new file mode 100644
index 0000000..4c21ec5
--- /dev/null
+++ b/blog/php-basic/string.md
@@ -0,0 +1,165 @@
+# 字符串 String
+
+## 字符串类型
+
+- 单引号字符串
+- 双引号字符串
+- nowdoc 字符串
+- heredoc 字符串
+
+示例
+
+```php
+<?php
+
+// 1、单引号字符串
+$str1 = 'hello world';
+
+var_dump($str1);
+// string(11) "hello world"
+
+// 2、双引号字符串
+$str2 = "hello world";
+
+var_dump($str2);
+// string(11) "hello world"
+
+// 3、nowdoc
+$str2 = <<<'EOD'
+hello world
+EOD;
+
+var_dump($str2);
+// string(11) "hello world"
+
+
+// 4、heredoc
+$str1 = <<<EOD
+hello world
+EOD;
+
+var_dump($str1);
+// string(11) "hello world"
+
+```
+
+## 字符串转义
+
+系统会特殊处理：反斜杠 + 字母
+
+例如：
+
+```
+\r\n 回车换行
+```
+
+PHP 中常用的转义字符
+
+```
+\'  在单引号字符串中显示单引号
+\"  在双引号字符串中显示双引号
+\r  回车（回到当行的行首）
+\n  换行
+\t  tab
+\$  $在PHP中作为变量符号
+
+```
+
+## 单引号和双引号的区别
+
+1、单引号中能够识别`\'`, 而双引号中不能识别`\'`
+
+```php
+<?php
+
+
+$str1 = 'hello \'world';
+$str2 = "hello \'world";
+
+var_dump($str1);
+// string(12) "hello 'world"
+var_dump($str2);
+// string(13) "hello \'world"
+
+```
+
+2、单引号中不能识别变量，而双引号中能识别`$`，解析变量
+
+- 变量本省需要与后面内容有区分，保证变量独立性
+- 使用变量标识符区分，加一组大括号`{}`
+
+```php
+<?php
+
+$a = 'Tom';
+
+$str1 = 'hello $a world';
+var_dump($str1);
+// string(14) "hello $a world"
+
+$str2 = "hello $a world";
+var_dump($str2);
+// string(15) "hello Tom world"
+
+$str3 = "hello $aworld";
+var_dump($str3);
+// PHP Notice:  Undefined variable: aworld
+
+$str4 = "hello {$a}world";
+var_dump($str4);
+// string(14) "hello Tomworld"
+
+```
+
+## 结构化定义字符串变量的规则
+
+1. 结构化定义字符串对应的边界符有条件
+   - 上边界符后面不能有任何内容
+   - 下边界符必须最左边顶格
+   - 下边界符后面只能跟符号，不能跟任何字符
+2. 结构化定义字符串的内部（边界符之间）的所有内容都是字符串本身
+
+
+```php
+<?php
+$str1 = <<<EOD
+hello world
+EOD;
+
+var_dump($str1);
+// string(11) "hello world"
+
+```
+
+## 字符串长度
+
+```php
+strlen(string $string): int
+```
+
+示例
+
+```php
+<?php
+
+$str1 = 'hello world';
+$str2 = '你好世界'; // 中文在utf8字符集下占3个字节
+
+var_dump(strlen($str1)); // int(11)
+var_dump(strlen($str2)); // int(12)
+```
+
+多字节字符串扩展模块 mbstring(Multi String)
+
+```php
+<?php
+
+$str1 = 'hello world';
+$str2 = '你好世界';
+
+var_dump(mb_strlen($str1)); // int(11)
+var_dump(mb_strlen($str2)); // int(4)
+
+```
+
+https://www.bilibili.com/video/BV18x411H7qD?p=79&spm_id_from=pageDriver
-- 
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