PHP - Manual: elseif/else if

2024-11-22

elseif/else if

(PHP 4, PHP 5, PHP 7, PHP 8)

elseif，和此名称暗示的一样，是 if 和 else 的组合。和 else 一样，它延伸了 if 语句，可以在原来的 if 表达式值为 false 时执行不同语句。但是和 else 不一样的是，它仅在 elseif 的条件表达式值为 true 时执行语句。例如以下代码将根据条件分别显示 a is bigger than b，a equal to b 或者 a is smaller than b：


<?php
if ($a > $b) {
    echo "a is bigger than b";
} elseif ($a == $b) {
    echo "a is equal to b";
} else {
    echo "a is smaller than b";
}
?>

在同一个 if 语句中可以有多个 elseif 部分，其中第一个表达式值为 true（如果有的话）的 elseif 部分将会执行。在 PHP 中，也可以写成“else if”（两个单词），它和“elseif”（一个单词）的行为完全一样。句法分析的含义有少许区别（如果你熟悉 C 语言的话，与之行为相同），但是底线是两者会产生完全一样的行为。

elseif 的语句仅在之前的 if 和所有之前 elseif 的表达式值为 false，并且当前的 elseif 表达式值为 true 时执行。

注意: 必须要注意的是 elseif 与 else if 只有在类似上例中使用花括号的情况下才认为是完全相同。如果用冒号来定义 if/elseif 条件，那就不能用两个单词的 else if，否则 PHP 会产生解析错误。


<?php

/* 不正确的使用方法： */
if ($a > $b):
    echo $a." is greater than ".$b;
else if ($a == $b): // 将无法编译
    echo "The above line causes a parse error.";
endif;


/* 正确的使用方法： */
if ($a > $b):
    echo $a." is greater than ".$b;
elseif ($a == $b): // 注意使用了一个单词的 elseif
    echo $a." equals ".$b;
else:
    echo $a." is neither greater than or equal to ".$b;
endif;

?>

add a note

User Contributed Notes 3 notes

down

Vladimir Kornea ¶

15 years ago


The parser doesn't handle mixing alternative if syntaxes as reasonably as possible.

The following is illegal (as it should be):

<?
if($a):
    echo $a;
else {
    echo $c;
}
?>

This is also illegal (as it should be):

<?
if($a) {
    echo $a;
}
else:
    echo $c;
endif;
?>

But since the two alternative if syntaxes are not interchangeable, it's reasonable to expect that the parser wouldn't try matching else statements using one style to if statement using the alternative style. In other words, one would expect that this would work:

<?
if($a):
    echo $a;
    if($b) {
      echo $b;
    }
else:
    echo $c;
endif;
?>

Instead of concluding that the else statement was intended to match the if($b) statement (and erroring out), the parser could match the else statement to the if($a) statement, which shares its syntax.

While it's understandable that the PHP developers don't consider this a bug, or don't consider it a bug worth their time, jsimlo was right to point out that mixing alternative if syntaxes might lead to unexpected results.

down

-3

mparsa1372 at gmail dot com ¶

1 year ago


The if...elseif...else statement executes different codes for more than two conditions.

Syntax:

if (condition) {
  code to be executed if this condition is true;
} elseif (condition) {
  code to be executed if first condition is false and this condition is true;
} else {
  code to be executed if all conditions are false;
}

Example:
Output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":

<?php
$t = date("H");

if ($t < "10") {
  echo "Have a good morning!";
} elseif ($t < "20") {
  echo "Have a good day!";
} else {
  echo "Have a good night!";
}
?>

down

-27

qualitycoder ¶

7 years ago


The reason 'else if' (with a space) works with traditional syntax and not colon syntax is because of a technicality.

<?php
  if($var == 'Whatever') {

  } else if($var == 'Something Else') {

  } 
?>

In this instance, the 'else if' is a shorthand/inline else statement (no curly braces) with the if statement as a body. It is the same things as:

<?php
  if($var == 'Whatever') {

  } else {
      if($var == 'Something Else') {

      }
  }
?>

If you were to write this with colon syntax, it would be:

<?php
  if($var == 'Whatever'):

  else:
      if($var == 'Something Else'):

      endif;
  endif;
?>

add a note

官方地址：https://www.php.net/manual/en/control-structures.elseif.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 修改图片大小支持php7的性能采集扩展 [鸟哥]PHP FFI详解 - 一种全新的PHP扩展方式 [原创]诡异的php-fpm超时问题 php扩展开发 PHP7 mcrypt替代方案

略微加速

PHP官方手册 - 互联网笔记

elseif/else if

User Contributed Notes 3 notes