preg_match函数无法正常工作

Question

I am trying to filter all the letters and special characters, and only allow numbers. But whenever I pass a 0 as a variable, it is returning me false.

 $string = 0;
   if(preg_replace('/[^0-9]/', '', $string) == true){
      echo 'True';
   }else{
      echo 'False';
   }

Answer 1

preg_replace

If matches are found, the new subject will be returned, otherwise subject will be returned unchanged or NULL if an error occurred.

When you check preg_replace('/[^0-9]/', '', $string) == true it is checking the string '0' after it has been stripped of all non-numeric characters (still '0') and seeing if it evaluates to TRUE. The string '0' and the int 0 both evaluate to FALSE. I.e '0' == FALSE && 0 == FALSE. This is why your condition is returning FALSE since '0' == FALSE.

You can change your condition to this instead: preg_replace('/[^0-9]/', '', $string) != ''

Now you will be checking to see if your string is empty after filtering out all non-numeric characters I.e if your string contained only non-numeric characters it would return FALSE.