PHP strtoupper() Function: Syntax, Parameters, Return Value, Usage Examples, and Important Notes

In PHP, the strtoupper() function converts all characters in a string to uppercase. It accepts a string as input and returns the transformed string.

strtoupper() Function Syntax

strtoupper(string $string)

Parameter Description:

$string

: required. The string to be converted to uppercase.

Return Value:

Returns a new string where every character of the original string has been converted to uppercase.

Usage Examples

$string = "Hello World";  
$uppercaseString = strtoupper($string);  
echo $uppercaseString;  // Output: HELLO WORLD

In this example, strtoupper() converts the string "Hello World" to uppercase, stores the result in $uppercaseString, and then outputs it.

Notes

strtoupper()

is case‑sensitive and works based on ASCII values, converting lowercase letters to their uppercase equivalents while leaving existing uppercase letters unchanged.

Non‑alphabetic characters such as numbers or punctuation are not altered.

The function can handle multibyte characters, including UTF‑8 encoded strings, making it useful for internationalization (i18n) and localization (l10n) scenarios.

strtoupper() Function Usage

Example 1: Convert the Entire String to Uppercase

$string = "Hello World";  
$uppercaseString = strtoupper($string);  
echo $uppercaseString;  // Output: HELLO WORLD

Example 2: Convert Only Part of the String to Uppercase

$string = "Hello World";  
$uppercaseString = strtoupper(substr($string, 6));  
echo $uppercaseString;  // Output: WORLD

Example 3: Convert the First Letter of Each Word to Uppercase

$string = "hello world";  
$titleCaseString = strtoupper(wordwrap($string, 5, " ", true));  
echo $titleCaseString;  // Output: HELLO world

Example 4: Convert All Words to Uppercase Using a Regular Expression

$string = "hello world";  
$allUpperCaseString = strtoupper(preg_replace('/\b\w+\b/', '${0,}', $string));  // Use regex to convert words to uppercase  
echo $allUpperCaseString;  // Output: HELLO WORLD (same as strtoupper result)

Example 5: Handle Multibyte Characters (e.g., UTF‑8 Strings)

$string = "你好世界"; // UTF‑8 encoded string containing Chinese characters  
$uppercaseString = strtoupper($string); // Convert Chinese characters to uppercase  
echo $uppercaseString; // Output: 你好世界 (same as strtoupper result)

Summary

The strtoupper() function in PHP is highly useful for converting all characters of a string to uppercase, which aids in case‑insensitive text processing, generating HTML tags, handling filenames and URLs, and forming database queries. It also supports multibyte characters, making it suitable for internationalized applications.

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