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WordPress

_mb_strlen( string $str, string|null $encoding = null ): int

Since
4.2.0
Source
wp-includes/compat.php:375
Internal compat function to mimic mb_strlen().

Description

Only supports UTF-8 and non-shifting single-byte encodings. For all other encodings expect the counts to be wrong. When the given encoding (or the blog_charset if none is provided) isn’t UTF-8 then the function returns the byte-count of the provided string.

Compatibility

WordPress
since 4.2.0
PHP
7.4–8.6-dev
  • 6.7.7
  • 6.8.8
  • 6.9.7
  • 7.0.4
  • 7.1.0

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$strstring
The string to retrieve the character length from.
$encodingstring|nulloptional
Count characters according to this encoding.
Default is to consult blog_charset.Default: null

Return value

int
Count of code points if UTF-8, byte length otherwise.

Performance profile

How much work a call to _mb_strlen() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class
Moderate

Reads stored settings via get_option(), cached per request but not free on a cold cache.

Scaling
Constant

No loop in the body: the same number of instructions runs whatever you pass in.

Instructions
9–15

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 17.

Plugin surface
None

Nothing here hands control to plugin code.

Called by
1

1 place in core call this, so the cost is paid more often than your own code shows.

What it touches

  • optionoption read or writeget_option()called directly
  • hookthird-party callbacksapply_filters()one call below _mb_strlen()
  • cacheobject cachewp_cache_get()one call below _mb_strlen()
  • serializeserialisationmaybe_unserialize()one call below _mb_strlen()

Further down the call graph this can also reach query and transient. Those are the worst case, several calls deep and usually down an error path, not what a normal call pays.

What one call costs · 4 distinct outcomes

One number would be a lie: the work depends on which branch runs. These are every distinct cost _mb_strlen() can have, taken from its control-flow graph on PHP 8.5.

WhenInstructionsCalls it makes
!_is_utf8_charset()9_is_utf8_charset()
_is_utf8_charset()11_is_utf8_charset(), _wp_utf8_codepoint_count()
!_is_utf8_charset()13get_option(), _is_utf8_charset()
_is_utf8_charset()15get_option(), _is_utf8_charset(), _wp_utf8_codepoint_count()

Across PHP versions

PHPCompiledExecutedBranchesNotes
8.6-dev169–1421 fewer instruction than PHP 8.5
8.5179–152
8.4179–152
8.3179–152
8.2179–152
8.1179–152
7.4179–152

An instruction is not a fixed amount of time, so a matching count is not necessarily the same speed; what it rules out is a difference in the work itself.

Uses · 3

Used by · 1

Source code

View on Trac View on GitHub 

function _mb_strlen( $str, $encoding = null ) {	return _is_utf8_charset( $encoding ?? get_option( 'blog_charset' ) )		? _wp_utf8_codepoint_count( $str )		: strlen( $str );}

Changelog

Introduced in 4.2.0. Unchanged from 6.7.7 through 7.1.0.

  1. 6.7.7
  2. 6.8.8
  3. 6.9.7
  4. 7.0.4
  5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

Parsed data
Generated from the wordpress-develop 7.1.0 tag, from src/wp-includes/compat.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.
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