How to convert lowercase string to uppercase in php

In PHP, there are many ways to convert lowercase characters to uppercase characters. In this article, we will introduce some commonly used methods.

1. strtoupper() function

The strtoupper() function is PHP’s built-in function, used to convert lowercase letters in a string to uppercase letters. Its syntax is as follows:

string strtoupper ( string $string )

Where, $string is the string that needs to be converted, and the function will return a string in which all lowercase characters are converted to uppercase characters.

For example:

$lower = "hello world";
$upper = strtoupper($lower);
echo $upper; // 输出结果为：HELLO WORLD

2. mb_strtoupper() function

If your string contains multi-byte characters, the strtoupper() function may cause some problems . In this case, we can use the mb_strtoupper() function. This function uses UTF-8 encoding and handles multibyte characters correctly. Its syntax is as follows:

string mb_strtoupper ( string $string [, string $encoding = mb_internal_encoding() ] )

Among them, $string is the string that needs to be converted, and $encoding is the encoding type that needs to be converted. If the $encoding parameter is not passed, this function will use the default encoding returned by the mb_internal_encoding() function.

For example:

$lower = "你好，world！";
$upper = mb_strtoupper($lower);
echo $upper; // 输出结果为：你好，WORLD！

3. Use ASCII values

If you don’t want to use the built-in function, you can manually convert lowercase characters to uppercase characters. In ASCII encoding, the ASCII range for lowercase letters is 97-122, and the ASCII range for uppercase letters is 65-90. So you can use the following method to convert:

function toUpper($str) {
    $len = strlen($str);
    for ($i = 0; $i < $len; $i++) {
        $ascii = ord($str[$i]);
        if ($ascii >= 97 && $ascii <= 122) {
            $str[$i] = chr($ascii - 32);
        }
    }
    return $str;
}

$lower = "hello world";
$upper = toUpper($lower);
echo $upper; // 输出结果为：HELLO WORLD

This method will loop through each character in the string and subtract 32 from the ASCII value of the lowercase character to convert it to the ASCII of the uppercase character value.

Summary

These are the common methods for converting lowercase characters to uppercase characters: using the strtoupper() function, using the mb_strtoupper() function to handle multi-byte characters, and manually converting ASCII values. Just choose the appropriate method according to your needs.

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