How to implement PHP to only retain numbers?

#How to implement PHP to only retain numbers?

1. Use regular expressions to match all numbers and extract them, or replace characters that are not numbers;

<?php
    $str=&#39;acc123nmnm4545&#39;;
    if(preg_match(&#39;/\d+/&#39;,$str,$arr)){
       echo $arr[0];
    }
?>

2. Split the string into an array and traverse it The array determines whether each character is a number, and if so, it can be extracted.

function findNum($str=''){
$str=trim($str);
if(empty($str)){return '';}
$temp=array('1','2','3','4','5','6','7','8','9','0');
$result='';
for($i=0;$i<strlen($str);$i++){
if(in_array($str[$i],$temp)){
$result.=$str[$i];
}
}
return $result;
}

function findNum($str=''){
$str=trim($str);
if(empty($str)){return '';}
$result='';
for($i=0;$i<strlen($str);$i++){
if(is_numeric($str[$i])){
$result.=$str[$i];
}
}
return $result;
}

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