PHP - Manual: 字符串运算符

2024-11-20

字符串运算符

有两个字符串（string）运算符。第一个是连接运算符（“.”），它返回其左右参数连接后的字符串。第二个是连接赋值运算符（“.=”），它将右边参数附加到左边的参数之后。更多信息见赋值运算符。


<?php
$a = "Hello ";
$b = $a . "World!"; // 现在 $b 包含 "Hello World!"

$a = "Hello ";
$a .= "World!";     // 现在 $a 包含 "Hello World!"
?>

参见

add a note

User Contributed Notes 7 notes

down

215

K.Alex ¶

9 years ago


As for me, curly braces serve good substitution for concatenation, and they are quicker to type and code looks cleaner. Remember to use double quotes (" ") as their content is parced by php, because in single quotes (' ') you'll get litaral name of variable provided:

<?php

 $a = '12345';

// This works:
echo "qwe{$a}rty"; // qwe12345rty, using braces
echo "qwe" . $a . "rty"; // qwe12345rty, concatenation used

// Does not work:
echo 'qwe{$a}rty'; // qwe{$a}rty, single quotes are not parsed
echo "qwe$arty"; // qwe, because $a became $arty, which is undefined

?>

down

172

anders dot benke at telia dot com ¶

18 years ago


A word of caution - the dot operator has the same precedence as + and -, which can yield unexpected results. 

Example:

<php
$var = 3;

echo "Result: " . $var + 3;
?>

The above will print out "3" instead of "Result: 6", since first the string "Result3" is created and this is then added to 3 yielding 3, non-empty non-numeric strings being converted to 0.

To print "Result: 6", use parantheses to alter precedence:

<php
$var = 3;

echo "Result: " . ($var + 3); 
?>

down

102

Stephen Clay ¶

16 years ago


<?php 
"{$str1}{$str2}{$str3}"; // one concat = fast
  $str1. $str2. $str3;   // two concats = slow
?>
Use double quotes to concat more than two strings instead of multiple '.' operators.  PHP is forced to re-concatenate with every '.' operator.

down

hexidecimalgadget at hotmail dot com ¶

13 years ago


If you attempt to add numbers with a concatenation operator, your result will be the result of those numbers as strings.

<?php

echo "thr"."ee";           //prints the string "three"
echo "twe" . "lve";        //prints the string "twelve"
echo 1 . 2;                //prints the string "12"
echo 1.2;                  //prints the number 1.2
echo 1+2;                  //prints the number 3

?>

down

mariusads::at::helpedia.com ¶

13 years ago


Be careful so that you don't type "." instead of ";" at the end of a line.

It took me more than 30 minutes to debug a long script because of something like this:

<?
echo 'a'.
$c = 'x';
echo 'b';
echo 'c';
?>

The output is "axbc", because of the dot on the first line.

down

-42

Rafael Serna ¶

3 years ago


Please note that concatenating an array item value using the  key => value syntax will result in a parse error if there are one or more spaces bewteen the concatenation operator (.) :

<?php

$elements = [
    'id' => 63,
    'name' => '{"name": "'. str_repeat("a", 1000) .'"}' // <-- Parse error (there are spaces surrounding string_repeat)
];

$elements = [
    'id' => 63,
    'name' => '{"name": "'.str_repeat("a", 1000).'"}' // <-- OK
];

down

-55

Joseph Alvini ¶

3 years ago


Concatenation inside of a for/foreach loop. Great for adding onto a string.

function Coffee($string){
    $arr = ["Loves", "Coffee", "With", "His", "Donuts"];
  
    foreach($arr as $items){
          $string  .= ' ' . $items;
    }
    
    return $string;
}

echo Coffee("Joe");

add a note

官方地址：https://www.php.net/manual/en/language.operators.string.php

有任何技术问题请点击这里网站运营推广招聘

IT PHP 编程语言 Linux 开发编程科技 Elasticsearch HTML/CSS/XML 网络 JAVA NoSQL 数据库面试 C/C++ Golang Git 算法操作系统正则表达式 Redis 互联网 MySql JavaScript 运维软件国际架构设计 Mac OS TCP/IP Excel Vim Windows Socket Oracle VR MongoDB Python 运营 MemCache 商业硬件电子娱乐设计 nginx 摄影游戏 WordPress HTTP 团建数码电器

php7 安装fileinfo扩展 preg_split — 通过一个正则表达式分隔字符串 php位值,解决 PHP 中 usort 在值相同时改变原始位置的问题 [PHP] inet_pton/inet_ntop IP地址转换函数 array_multisort() 多字段排序 PHPMailer设置utf8 PHPMailer字符集CharSet ADORecordSet对象 PHP 8.1 [鸟哥]PHP_INT_MIN 和 -9223372036854775808 adodb手册 opcache预加载 Composer的Packagist资源 mysql面试题 php中几种注释规范 php 修改图片大小 PHP获取指定函数定义在哪个文件中及行号 PHP7 mcrypt替代方案 Packagist / Composer 中国全量镜像 laravel框架查看sql语句方式 PHP json解析（json_decode）页面工具

略微加速

PHP官方手册 - 互联网笔记

字符串运算符

参见

User Contributed Notes 7 notes