strlen()

(PHP 4, PHP 5, PHP 7)

获取字符串长度

说明

返回给定的字符串 $string 的长度。

参数

$string

需要计算长度的字符串。

返回值

成功则返回字符串 $string 的长度；如果 $string 为空，则返回 0。

更新日志

范例

strlen() 范例

注释

Note:

strlen() returns the number of bytes rather than the number of characters in a string.

Note:

strlen() returns NULL when executed on arrays, and an E_WARNING level error is emitted.

参见

• count()计算数组中的单元数目，或对象中的属性个数
• mb_strlen()获取字符串的长度

I want to share something seriously important for newbies or beginners of PHP who plays with strings of UTF8 encoded characters or the languages like: Arabic, Persian, Pashto, Dari, Chinese (simplified), Chinese (traditional), Japanese, Vietnamese, Urdu, Macedonian, Lithuanian, and etc.
As the manual says: "strlen() returns the number of bytes rather than the number of characters in a string.", so if you want to get the number of characters in a string of UTF8 so use mb_strlen() instead of strlen().
Example:

The easiest way to determine the character count of a UTF8 string is to pass the text through utf8_decode() first:

utf8_decode() converts characters that are not in ISO-8859-1 to '?', which, for the purpose of counting, is quite alright.

We just ran into what we thought was a bug but turned out to be a documented difference in behavior between PHP 5.2 & 5.3. Take the following code example:

// Begin Output:
Length: 0
Length: 0 
Length: 0
Null length is Zero 
Null length is still Zero 
!is_null(): $foo is probably null 
isset(): $foo is probably null 
!is_null(): $bar is truly an empty string 
isset(): $bar is truly an empty string 
// End Output
So it would seem you need either is_null() or isset() in addition to strlen() if you care whether or not the original value was null.

There's a LOT of misinformation here, which I want to correct! Many people have warned against using strlen(), because it is "super slow". Well, that was probably true in old versions of PHP. But as of PHP7 that's definitely no longer true. It's now SUPER fast!
I created a 20,00,000 byte string (~20 megabytes), and iterated ONE HUNDRED MILLION TIMES in a loop. Every loop iteration did a new strlen() on that very, very long string.
The result: 100 million strlen() calls on a 20 megabyte string only took a total of 488 milliseconds. And the strlen() calls didn't get slower/faster even if I made the string smaller or bigger. The strlen() was pretty much a constant-time, super-fast operation
So either PHP7 stores the length of every string as a field that it can simply always look up without having to count characters. Or it caches the result of strlen() until the string contents actually change. Either way, you should now never, EVER worry about strlen() performance again. As of PHP7, it is super fast!
Here is the complete benchmark code if you want to reproduce it on your machine:

if your text contain UTF8 character (arabic character for example), the mb_substr can use instead of strlen.
but if the string contain UTF16 (wmoji, smily) then you can use this method to get correct length:

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