Behavior Analysis of PHP ctype_upper Function with Non-Alphabetic Characters

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<p>Behavior Analysis of PHP ctype_upper Function with Non-Alphabetic Characters</p>
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<p>ctype_upper is a PHP function used to check if all alphabetic characters in a string are uppercase.</p>
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<p>Function prototype:</p>
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<p>bool ctype_upper(string $text)</p>
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<p>The function returns true if and only if the string is non-empty and all alphabetic characters are uppercase.</p>
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<p>If the string contains non-alphabetic characters, those characters do not affect the result,</p>
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<p>but an empty string will return false.</p>
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<p>Behavior analysis:<br>
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<p>// Example 1: Pure uppercase letters<br>
$str1 = "HELLO";<br>
var_dump(ctype_upper($str1)); // Output: bool(true)</p>
<p>// Example 2: Contains lowercase letters<br>
$str2 = "Hello";<br>
var_dump(ctype_upper($str2)); // Output: bool(false)</p>
<p>// Example 3: Contains numbers<br>
$str3 = "HELLO123";<br>
var_dump(ctype_upper($str3)); // Output: bool(true)  Non-alphabetic characters do not affect the check</p>
<p>// Example 4: Contains symbols<br>
$str4 = "HELLO!";<br>
var_dump(ctype_upper($str4)); // Output: bool(true)  Non-alphabetic characters do not affect the check</p>
<p>// Example 5: Empty string<br>
$str5 = "";<br>
var_dump(ctype_upper($str5)); // Output: bool(false)  Empty string returns false</p>
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<p>Key Takeaways:</p>
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<p>ctype_upper only checks alphabetic characters; uppercase letters return true.</p>
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<p>Non-alphabetic characters (such as numbers, punctuation, spaces) do not cause a false result.</p>
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<p>An empty string always returns false.</p>
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<p>If the string contains any lowercase letters, it returns false.</p>
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<p>Usage tips:</p>
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<p>When you need to strictly determine whether a string consists entirely of uppercase letters, you can directly use ctype_upper.</p>
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<p data-is-last-node="">If you want to ignore the effect of non-alphabetic characters, you can also use it directly without additional processing.<br>
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