mb_substr()

(PHP 4 >= 4.0.6, PHP 5, PHP 7)

获取部分字符串

说明

根据字符数执行一个多字节安全的substr()操作。位置是从$str的开始位置进行计数。第一个字符的位置是 0。第二个字符的位置是 1，以此类推。

参数

从该string中提取子字符串。

如果$start不是负数，返回的字符串会从$str第$start的位置开始，从 0 开始计数。举个例子，字符串'abcdef'，位置0的字符是'a'，位置2的字符是'c'，以此类推。

如果$start是负数，返回的字符串是从$str末尾处第$start个字符开始的。

$str中要使用的最大字符数。如果省略了此参数或者传入了NULL，则会提取到字符串的尾部。

$encoding参数为字符编码。如果省略，则使用内部字符编码。

返回值

mb_substr()函数根据$start和$length参数返回$str中指定的部分。

更新日志

参见

• mb_strcut()获取字符的一部分
• mb_internal_encoding()设置/获取内部字符编码

Passing null as length will not make mb_substr use it's default, instead it will interpret it as 0.

Instead use: 

Thanks Darien from /freenode #php for the following example (a little bit changed).
It just prints the 6th character of $string.
You can replace the digits by the same in japanese, chinese or whatever language to make a test, it works perfect.

(I couldn't replace 0123456789 by chinese numbers for example here, because it's automatically converted into latin digits on this website, look : 
零一二三四
五六七八九)
gilv

As you often need to iterate over UTF-8 characters inside a string, you might be tempted to use mb_substr($text,$i,1).
The problem with this is that there is no "magic" way to find $i-th character inside UTF-8 string, other than reading it byte by byte from the begining. Thus a loop which calls mb_substr($text,$i,1) N times for all possible N values of $i, will take much longer than expected. The larger the $i gets, the longer is the search for $i-th letter. As characters are between 1 to 6 bytes long, one can convince oneself, that the execution time of such loop is actually Theta(N^2), which can be really slow even for moderately long texts.
One way to work around it is to first split your text into an array of letters using some smart preprocessing, and only then iterate over the array.
Here is the idea:

As you can see, the Strings::letters($text) split the text recursively into two parts. Each level of the recursion requires time linear in the length of the string, and there is logarithmic number of levels, so the total runtime is O(N log N), which is still more than theoretically optimal O(N), but sadly this is the best idea I've got.

Note: If borders are out of string - mb_string() returns empty _string_, when function substr() returns _boolean_ false in this case.
Keep this in mind when using "===" comparisions.
Example code:

It's especially confusing when using mbstring with function overloading turned on.

I'm trying to capitalize only the first character of the string and tried some of the examples above but they didn't work. It seems mb_substr() cannot calculate the length of the string in multi-byte encoding (UTF-8) and it should be set explicitly. Here is the corrected version:

cheers!

you can make mb_substr working faster with long strings with usage of ucs-2 encoding.

output:
mb_substr, utf8: 0.26480984687805 . check: string(5) "ст " .
mb_substr, ucs2: 0.0048871040344238 . check: string(5) "ст " .

quick and dirty loop through multibyte string

Array
(
  [numeric] => numeric
  [alpha] => alpha
  [alphalower] => alphalower
  [alphaupper] => alphaupper
  [currency] => currency
  [ascii] => ascii
  [binary] => binary
)

A serious pitfall when using mb_substr() set to HTML-ENTITIES encoding is that the function performs a number of conversions before returning the value, the worst one being that html special characters are not just counted but decoded. 

First letter in upper case 

鹏仔微信 15129739599 鹏仔QQ344225443 鹏仔前端 pjxi.com 共享博客 sharedbk.com