Check if string is full-width Japanese. Useful when you need to validate a name field in Japanese.

gistfile1.php

function jpn_zenkaku_only($str) {

	$encoding = "UTF-8";
	
	// Get length of string
	$len = mb_strlen($str, $encoding);

	        
	// Check each character 
	for ($i = 0; $i < $len; $i++) {
		$char = mb_substr($str, $i, 1, $encoding);
    
		// Check for non-printable characters
		if (ctype_print($char)) {
			return false;
		}
	            
		// Convert to SHIFT-JIS to include kana characters
		$char = mb_convert_encoding($char, 'SJIS', $encoding);
    
		// Check if string lengths match
		if (strlen($char) === mb_strlen($char, 'SJIS')) {
			return false;
		}
	}
}