从字符串中提取数字（4个位置）

I would like to extract a number (4 positions) from a string which is stored in a database.

e.g. "Mountain guesthouse (2340m) in Radons" How is this to be done? It is possible that the number is like 2.340m

<?php

//$string = 'Mountain guesthouse (2340m) in Radons';    
//preg_match('#([0-9]+)m#is', $string, $matches);    
//$peak = number_format($matches[1], 0, ',', '.');

//EDIT
$string = 'Mountain guesthouse (23.40m) in Radons';    
$preg_match('#([0-9\.]+)m#is', $string, $matches);
$peak=$matches[1];

echo $peak . 'm'; # 23.40m

?>

Live: http://ideone.com/42RT4
Edit live: https://ideone.com/hNJxG

Your question is a little vague. Is m always a part of the number? Do you want to extract it too? Does the number always consist of 4 digits? The below matches any integer or floating point integer without scientific notation.

if (preg_match('/[0-9]*\.?[0-9]+/', $subject, $regs)) {
    $result = $regs[0];
    #check if . is present and if yes length must be 5 else length must be 4
    if (preg_match('/\./', $result) && strlen($result) == 5) {
      #ok found match with . and 4 digits
    }
    elseif(strlen($result) == 4){
       #ok found 4 digits without .
    }
}

preg_match('/\d\.?\d{3}/', $text, $matches);

Matches a number followed by an optional dot and 3 more numbers.

php > $text = "Mountain guesthouse (2340m) in Radons";
php > preg_match('/\d\.?\d{3}/', $text, $matches);
php > print_r($matches);
Array
(
    [0] => 2340
)

(Edited from @webarto's answer)

<?php

$string = 'Mountain guesthouse (23.40m) in Radons';

preg_match('#([0-9\.]+)m#is', $string, $matches);

$peak = $matches[1];

echo $peak . 'm'; # 2.340m

?>