substr 函数如何工作? [英] How substr function works?
问题描述
我在 php.net 中遇到过这段代码.
I have come across this code in php.net.
<?php
echo substr('abcdef', 1); // bcdef
echo substr('abcdef', 1, 3); // bcd
echo substr('abcdef', 0, 4); // abcd
echo substr('abcdef', 0, 8); // abcdef
echo substr('abcdef', -1, 1); // f
// Accessing single characters in a string
// can also be achieved using "square brackets"
$string = 'abcdef';
echo $string[0]; // a
echo $string[3]; // d
echo $string[strlen($string)-1]; // f
?>
substr('abcdef',1,3)
返回 'bcd'
,最后一个索引是 3,它返回 "bcd"
如果我执行 substr('abcdef',0,4)
返回 'abcd'
.但与第一个示例相比,我希望 substr('abcdef',0,3)
返回 'abcd'
.我在这里错过了什么.
substr('abcdef',1,3)
returns 'bcd'
, the last index is 3 and it returns "bcd"
and if I do substr('abcdef',0,4)
returns 'abcd'
. But I expected substr('abcdef',0,3)
to return 'abcd'
as compared to the first example. What am I missing here.
substr($string,$start,$last)
在 php 中是如何工作的?
How substr($string,$start,$last)
works in php?
对不起,我认为第三个参数不是长度和超出我理解的东西......由于我的 Java
背景抱歉.感谢所有评论和回答.
Sorry every body I thought 3rd param is not length and something beyond my understanding...due to my Java
background sorry. Thanks for all comments and answers.
推荐答案
substr()
is NOT substr($string, $start, $last)
它是 substr($string, $start, $length)
.所以 substr('abcdef', 0, 4)
返回 abcd
因为它从 0 (a) 开始,它有 4 个字母.
substr()
is NOT substr($string, $start, $last)
it's substr($string, $start, $length)
. So substr('abcdef', 0, 4)
returns abcd
because it starts at 0 (a) and it goes for 4 letters.
还有随机注释:echo substr('abcdef', -1, 1);
本质上是多余的,因为 -1 的长度只有 1,所以字符串也可能是:echo substr('abcdef', -1);
Also random note: echo substr('abcdef', -1, 1);
is inherently redundant since -1 only has a length of 1 so the string might as well be: echo substr('abcdef', -1);
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