PHP strtoupper Function: Convert Strings to Uppercase

Use strtoupper() function when you want to change all letters in a string to uppercase in PHP. It works with standard ASCII characters.

Understand the Uppercase Function (strtoupper) in PHP

The strtoupper() changes every letter in a string to its uppercase version. It does not touch numbers or symbols. It works on ASCII strings, so it may not handle accented or non-English characters as expected.

strtoupper($string)

You pass in a text. It gives you a new string in all uppercase.

Here is a quick example:

$name = "john doe";
$upper = strtoupper($name);
echo $upper;

The output:

JOHN DOE

This example takes a name with lowercase letters and turns it into full uppercase. The function does not change spaces or punctuation.

But, how strtoupper() handles numbers and symbols?

It leaves numbers and spaces alone. It only changes letters.

For example:

$text = "user123@example.com";
echo strtoupper($text);

The output:

USER123@EXAMPLE.COM

The numbers and the @ symbol stay the same.

You can use strtoupper() on both sides when you compare strings. That does not care about the case.

$userInput = "yes";
$answer = "YES";

if (strtoupper($userInput) === strtoupper($answer)) {
    echo "Match";
}

This makes the check work no matter how the user types their answer.

Difference Between strtoupper() and mb_strtoupper()

strtoupper() only works well with basic English characters. It may not convert everything if your text uses other languages or accents.

mb_strtoupper() handles multibyte characters like (é, ü, ç). You must use the correct encoding (usually UTF-8).

$text = "français";
echo strtoupper($text);         
echo mb_strtoupper($text);     

Output:

FRANÇAIS (wrong result)
FRANÇAIS (correct)

Examples of Uppercase Function in PHP

Convert an array of strings to uppercase:

$colors = ["red", "green", "blue"];
$upperColors = array_map("strtoupper", $colors);

print_r($upperColors);

Output:

["RED", "GREEN", "BLUE"]

This runs strtoupper() on every item in the array.

Uppercase multibyte strings with mb_strtoupper():

$text = "schön";
$upper = mb_strtoupper($text, "UTF-8");

echo $upper; 

Output:

SCHÖN

ö would stay lowercase without mb_strtoupper(). This function handles it the right way.

Normalize user input for email:

$email = "user@Example.com";
$cleanEmail = strtolower($email);

echo $cleanEmail;

Output:

user@example.com

You can combine strtolower() and strtoupper() based on your goal. Use strtolower() for emails, and strtoupper() for codes or labels.

Format product codes:

$code = "abc-123";
$code = strtoupper($code);

echo $code;

Output:

ABC-123

Product codes often need consistent casing. strtoupper() helps keep them uniform.

Wrapping Up

You learned how to use strtoupper() to convert strings to uppercase. You also saw how it behaves with symbols and arrays with multibyte text. Also, you now know when to use strtoupper() and when to switch to mb_strtoupper().

Here is a quick recap:

• Use strtoupper() for basic ASCII text
• Use mb_strtoupper() for non-English characters
• Combine with arrays and other functions for more control
• Helpful in case-insensitive checks and formatting

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