PHP mb_substr() Function: Definition, Parameters, Return Value, Usage Notes, and Examples

The PHP mb_substr() function is a multibyte‑aware substring function that correctly handles multibyte characters, avoiding issues that arise with standard string functions.

Function Definition

<code>mb_substr(string $str, int $start, int $length = null, string $encoding = null): string</code>

Parameter Explanation

$str : The input string to be sliced.

$start : The starting position. Positive values count from the beginning; negative values count from the end.

$length : The number of characters to extract. Positive values extract forward from the start; negative values extract backward from the end. If omitted, extraction continues to the end of the string.

$encoding : The character encoding. If provided, the function uses this encoding; otherwise it attempts to detect the encoding automatically.

Return Value

The function returns the extracted substring.

Important Notes

The function operates on multibyte character sequences, so ensure the input string is encoded accordingly before using mb_substr() .

Although the fourth parameter $encoding can be omitted, explicitly specifying the encoding (e.g., "UTF-8") is recommended for reliable results.

When using negative numbers, mb_substr() treats them differently from standard substring functions: a negative start position counts from the beginning of the string rather than from the end.

Example Usage

Extract a portion of a string

<code>$str = "Hello, 世界！";
$substring = mb_substr($str, 0, 5, "UTF-8"); // returns "Hello"
</code>

Extract from the end of a string

<code>$str = "Hello, 世界！";
$substring = mb_substr($str, -7, 5, "UTF-8"); // returns "世界"
</code>

Automatic encoding detection

<code>$str = "Hello, 世界！";
$substring = mb_substr($str, 0, 5); // returns "Hello"
</code>

Specify encoding explicitly

<code>$str = "你好，世界！";
$substring = mb_substr($str, 0, 5, "UTF-8"); // returns "你好"
</code>

When using mb_substr() , ensure the string is a multibyte sequence and specify the correct encoding to obtain accurate results.

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