How to know if the line is empty while reading char by char in PHP

Question

How do I differentiate between an empty line and an endofline in PHP while reading character by character. In short I want to know how to find an empty line while reading char by char. Let me know if anything is unclear with a comment. Thank you...

Answer 1

You can either collect the characters of the current line in a buffer and then count when you see the end of line.

$buffer = '';
while (($char = fgetc($fp)) !== false) {
    if ($char != '\n') {
        $buffer .= $char;
    } else {
        if (strlen($buffer) == 0) {
            echo "Empty line\n";
        } else {
            echo "Non-empty line\n";
        }

        $buffer = '';
    }
}

Or you keep a count of characters while you read, until you see the end of line

$count = 0;
while (($char = fgetc($fp)) !== false) {
    if ($char != '\n') {
        ++$count;
    } else {
        if ($count == 0) {
            echo "Empty line\n";
        } else {
            echo "Non-empty line\n";
        }

        $count = 0;
    }
}

As you can see, both versions are similar, it only depends on whether you need the line afterwards or not.

---

To consider \r, you can compensate when you see one immediately before a \n, e.g.

$cr = false;
$count = 0;
while (($char = fgetc($fp)) !== false) {
    if ($char != '\n') {
        $cr = false;
        ++$count;
        if ($char == "\r")
            $cr = true;
    } else {
        if ($cr)
            --$count;

        if ($count == 0) {
            echo "Empty line\n";
        } else {
            echo "Non-empty line\n";
        }

        $count = 0;
    }
}

$cr is true, if the previous character was a \r. So if you look at a newline and $cr is true, you have a CRLF and decrement the character count by one.

As an alternative, you can collect the whole line and trim whitespace before looking at the length

if (strlen(trim($buffer)) == 0) {
    echo "Empty line\n";
} else {
    echo "Non-empty line\n";
}

---

Even though not asked, reading a whole line and checking might be more efficient, e.g.

while (($buffer = fgets($fp)) !== false) {
    if (strlen(rtrim($buffer, "\n")) == 0) {
        echo "Empty line\n";
    } else {
        echo "Non-empty line\n";
    }
}