PHP比较两个相等的字符串失败

Question

today i have a problem with two strings. The first comes from an Function-Parameter, the second string i'm getting from a file.

I only see these characters: "703866200".

When i convert the two strings in ASCII-Chars, get this (I have the characters separated by dots):

My Function-Param: 55.48.51.56.54.54.50.48.48

String from File: 55.0.48.0.51.0.56.0.54.0.54.0.50.0.48.0.48

This means that the two strings are detected always different (strcmp).

Can anybody help me? - Is it an Encoding Problem, or what means that the second String is filled with zeros?

BTW, my string2ascii function:

function string_to_ascii($string){
    $ascii = NULL; 
    for ($i = 0; $i < strlen($string); $i++){
      $ascii .= ".".ord($string[$i]);
    }
    return($ascii);
}