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mb_strtoupper

mb_strtoupper($string, $encoding)

Converts all letters in a text to uppercase, accented letters included. The strtoupper() function handles only the letters a–z.

Parameters

$string – the text to convert.
$encoding – optional, the character encoding. The default is the value of mb_internal_encoding(), usually UTF-8.

Examples

echo mb_strtoupper("crème brûlée"); // CRÈME BRÛLÉE
// strtoupper does not convert accented letters
var_dump(strtoupper("été") === "ÉTÉ"); // bool(false)
var_dump(mb_strtoupper("été") === "ÉTÉ"); // bool(true)
// an uppercase first letter of text with accents
echo mb_strtoupper(mb_substr("élan", 0, 1)) . mb_substr("élan", 1); // Élan
// digits and other characters do not change
echo mb_strtoupper("café no. 5"); // CAFÉ NO. 5
// the German sharp s becomes two letters
echo mb_strtoupper("straße"); // STRASSE
echo mb_strlen("straße") . " and " . mb_strlen(mb_strtoupper("straße")); // 6 and 7
// conversion breaks HTML entities
echo mb_strtoupper("caf&eacute;"); // CAF&EACUTE;

Things to watch out for

For text with accents always use mb_strtoupper. The strtoupper() function does not convert accented letters and in PHP 7 it can damage UTF-8 text depending on the locale setting.
The length of the text can change. Since PHP 7.3 the German “ß” becomes “SS”, so do not rely on a fixed length of the result.
Do not convert text that already contains HTML tags or entities. é becomes an invalid entity. Convert the original text and only then escape it with htmlspecialchars().
When it is only about the look (a heading in capitals), keep the text in its original form and use text-transform: uppercase in CSS.
The function for an uppercase first letter (mb_ucfirst) exists only since PHP 8.4, in older versions the code from the example replaces it.

Related functions:
strtoupper()
mb_strtolower()
mb_convert_case()