ソフトウェアエンジニアの技術ブログ：Software engineer tech blog

There is a trouble that it is not goes well at reading one line regular expression.
I would like to code if only one dot contained in a line, issue an alert.

$file = fopen("test.txt", "r");

if($file){
	while($line = fgets($file)){

		if(preg_match('/^.$/', $line)){
			echo "please write again.<br>";
		} else {
			echo "OK<br>";
		}

	}
}
fclose($file);

Regular expression does not work well in this code.

add half-width dot in the regular expression

if($file){
	while($line = fgets($file)){

		if(preg_match('/^..$/', $line)){
			echo "please write again.<br>";
		} else {
			echo "OK<br>";
		}

	}
}

A half-size dot in a regular expression means an arbitrary one character.

How to count the number of characters, number of bytes, character width (apparent length) of a character string in PHP?

1. strlen
function strlen
Generally, to know the number of bytes, use strlen.

mb_internal_encoding('UTF-8');
$char = 'To die: to sleep No more; and by a sleep to say we end. The heart-ache and the thousand natural shocks. That flesh is heir to, tis a consummation Devoutly to be wishd. ';
echo strlen($char);

168

2. mb_strlen
function mb_strlen
Also, use mb_strlen to distinguish between full-width and half-width characters and count the number of characters.

mb_internal_encoding('UTF-8');
$char = '名前(カタカナ)';

echo mb_strlen($char);

3. mb_strwidth
function mb_strwidth
Use mb_strwidth to count character width(apparent length).

mb_internal_encoding('UTF-8');
$char = 'おはようございます。';

echo mb_strwidth($char);

Let’s put emoji and count it.

mb_internal_encoding('UTF-8');
$char = 'こんにちは😀';

echo strlen($char);

-> 19
it is as expected.

Then, let’s display an alert if it is more than 10 bytes.

mb_internal_encoding('UTF-8');
$char = 'こんにちは😀';

// echo strlen($char);
if(strlen($char) > 10){
	echo "this is more than 10 byte, please write again";
} else {
	echo "confirmed.";
}

-> this is more than 10 byte, please write again

Perfect job, am I.

Some of the pictograms and Chinese characters are 4bytes of UTF-8 characters, and cannot be saved depending on the version of mysql and character code. I think there is something I want to check that there are more characters than the UTF-8 range in the string.

let’s look at sample, cherry blossom is 4 byte characters.

mb_internal_encoding('UTF-8');
$char = 'abcdefgあいうえお🌸';

echo preg_replace('/[\xF0-\xF7][\x80-\xBF][\x80-\xBF][\x80-\xBF]/', '', $char);

abcdefgあいうえお
Wow, it’s impressive.

Ok then, I want to display an alert if 4-byte characters are included.
Let’s see regular expression below.

mb_internal_encoding('UTF-8');
$char = 'abcdefgあいうえお';
// $char = 'abcdefgあいうえお🌸';

// echo preg_replace('/[\xF0-\xF7][\x80-\xBF][\x80-\xBF][\x80-\xBF]/', '', $char);

if(preg_match('/[\xF0-\xF7][\x80-\xBF][\x80-\xBF][\x80-\xBF]/', $char)){
	echo "alert, it included 4 byte";
} else {
	echo "there is no 4 byte charcter";
}

Oh my goodness.
“just trust yourself. surely, the way to live is coming. Goethe”