wp_check_invalid_utf8() │ WP 2.8.0

Checks for invalid UTF8 in a string.

Used By: sanitize_text_field(), esc_html()

No Hooks.

Return

String. The checked text.

Usage

wp_check_invalid_utf8( $string, $strip );
$string(string) (required)
The text which is to be checked.
$strip(true|false)
Whether to attempt to strip out invalid UTF8.
Default: false

Changelog

Since 2.8.0 Introduced.

Code of wp_check_invalid_utf8() WP 5.9.3

wp-includes/formatting.php 
function wp_check_invalid_utf8( $string, $strip = false ) {
	$string = (string) $string;

	if ( 0 === strlen( $string ) ) {
		return '';
	}

	// Store the site charset as a static to avoid multiple calls to get_option().
	static $is_utf8 = null;
	if ( ! isset( $is_utf8 ) ) {
		$is_utf8 = in_array( get_option( 'blog_charset' ), array( 'utf8', 'utf-8', 'UTF8', 'UTF-8' ), true );
	}
	if ( ! $is_utf8 ) {
		return $string;
	}

	// Check for support for utf8 in the installed PCRE library once and store the result in a static.
	static $utf8_pcre = null;
	if ( ! isset( $utf8_pcre ) ) {
		// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		$utf8_pcre = @preg_match( '/^./u', 'a' );
	}
	// We can't demand utf8 in the PCRE installation, so just return the string in those cases.
	if ( ! $utf8_pcre ) {
		return $string;
	}

	// phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged -- preg_match fails when it encounters invalid UTF8 in $string.
	if ( 1 === @preg_match( '/^./us', $string ) ) {
		return $string;
	}

	// Attempt to strip the bad chars if requested (not recommended).
	if ( $strip && function_exists( 'iconv' ) ) {
		return iconv( 'utf-8', 'utf-8', $string );
	}

	return '';
}

sanitize_

Sanitizing, Escaping