大括号是PHP中最常见、最容易被忽略也是最不可或缺的一部分，本文整理除了“{}”的三大作用，希望对读者有所帮助。
“{}”三大作用分别是：
将多个独立语句合并为一个复合语句，例如 if … else …中经常如此使用
在变量间接引用中进行定界，避免歧义。例如 ${$my_var[8]}与${$my_var}[8]的区分
用于指示字符串变量中的单个字符（下标从0开始）。
比如说：“my_string”=“joker”；
不加似乎也可以,加{}是什么意思呢?
还有字段名 为什么要以“包括呢?
至少便于阅读嘛~~~''是insert into语句要求的，因为字符串要成对出现嘛
加{}有时候是为了防止变量名和后面的字符串连在一起嘛
例如
{$cid}dd
如果cid=aa
那么{$cid}dd=aadd
不加的话你自己看看了$ciddd，岂不变成了ciddd变量了~~
// The following is okay as it's inside a string. Constants are not // looked for within strings so no E_NOTICE error here print "Hello $arr[fruit]"; // Hello apple // With one exception, braces surrounding arrays within strings // allows constants to be looked for print "Hello {$arr[fruit]}"; // Hello carrot print "Hello {$arr['fruit']}"; // Hello apple
PHP 变量后面加上一个大括号{}，里面填上数字，就是指PHP 变量相应序号的字符。
例如：
$str = 'hello';
echo $str{0}; // 输出为 h
echo $str{1}; // 输出为 e
如果要检查某个字符串是否满足多少长度，可以考虑用这种大括号（花括号）加isset 的方式替代 strlen 函数，因为 isset 是语言结构，strlen 是函数，所以使用 isset 比使用strlen 效率更高。
比如判断一个字符串的长度是否小于 5：
if ( !isset ( $str{5} ) ) 就比 if (strlen ( $str ) < 5 )好。
下面几个比较能说明原因的解释是:
表示{}里面的是一个变量 ,执行时按照变量来处理
在字符串中引用变量使用的特殊包括方式，这样就可以不使用.运算符，从而减少代码的输入量了。 其实输出那块是等 同于print "hello ".$arr['fruit'];
php中大括号的作用，如下：
一、不管什么程序，function name(){}, for(){},….这太多了，不说也知道什么用了。
二、$str{4}在字符串的变量的后面跟上{}刚大括号和中括号一样都是把某个字符串变量当成数组处理
三、{$val}，这时候大括号起的作用就是，告诉PHP，括起来的要当成变量处理。
$arr=array(0=>123,'name'=>'小猪'); foreach($array as $k=>$v){ echo "select * from blog_blogs where blog_tags like '%{$arr[$k]}%'order by blog_id"; //加一个大括号只是将作 为变量的标志符 } echo '<br/ ><br/><br/><br/><br/><br/><br/ >'; foreach($array as $k=>$v){ echo "select * from blog_blogs where blog_tags like'%{{$arr[$k]}}%' order by blog_id"; //加两个大括号，外面的 将作为普通的字符 } //用大括号来区分变量 //echo "$arr['name']";//用此句会报语法错误 echo "{$arr['name']}";//此句正常，大括号内的字符将作为变量来处理 //$str{4}在字符串的变量的后面跟上{}大括号和中括号一样都是把某个字符串变量当成数组处理 $str = 'abcdefg'; echo $str{4};
以上就是大括号在php中的一些作用的详细内容，更多请关注求知技术网其它相关文章！
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