How to detect if a string contains uppercase letters in php

Two methods: 1. Use strlen() and ord() to check whether each letter is uppercase, the syntax "for($i=0;$i=ord('A')&&ord($str[$i])

The operating environment of this tutorial: windows7 system, PHP8.1 version, DELL G3 computer

php checks whether the string contains Capital letters can also be understood as determining whether all letters in a string are lowercase. You can use the following two methods to judge.

Method 1: strlen() ord() function checks whether each letter in the string is uppercase one by one

• Use first Use the strlen() function to get the length of the string and then loop out the individual letters

• Then use the php ord() function to check whether each letter is uppercase

  ord () function can return the ASCII value of a character.

  The ASCII value ranges from 65 to 90, which are 26 uppercase English letters, and the ASCII values ​​from 97 to 122, which represent 26 lowercase English letters.

Just get the ASCII value of the character and check whether it is between 65 and 90.

PHP custom function:

/**
 * # 检测字符串中是否含有大写字母
 * @param string 要判断的字符串
 * 
 * @return bool 含有大写字母返回 TRUE 否则返回 FALSE
 */
function is_bigstr($str)
{
    for ($i = 0; $i < strlen($str); $i++) {
        if (ord($str[$i]) >= ord(&#39;A&#39;) &&
            ord($str[$i]) <= ord(&#39;Z&#39;)) {
            return true;
        }
    }
    return false;
}

Function call:

var_dump(is_bigstr('hello'));
// false
var_dump(is_bigstr('Hello'));
// true

Method 2: Use the preg_match() function to match the regular pattern Expression to detect whether it contains uppercase letters

The preg_match function is used to perform a regular expression pattern match and will return the number of matches of the pattern (0 or 1). 0 means no match, 1 means there is a match.

The regular expression used is: /[A-Z]/, used to find uppercase letters

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;);  
function is_bigstr($str)
{
    if(preg_match(&#39;/[A-Z]/&#39;, $str)){
    	echo &#39;有大写字母！<br>&#39;;
	}else{
	    echo &#39;没有大写字母！<br>&#39;;
	}
}
is_bigstr(&#39;hello&#39;);
is_bigstr(&#39;Hello&#39;);
?>

• There are no uppercase letters in the first string, so there is no match and 0 is returned; and 0 will be automatically converted to FALSE in () of the if statement; therefore, the code in else is executed.
  

• There are uppercase letters in the second string, so there is a match and 1 is returned; and 1 will be automatically converted to TRUE in () of the if statement; therefore, directly Code after executing if.

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