PHP验证信用卡卡号是否正确函数


            可以使用以下PHP函数，验证一个卡号是否是信用卡：





function validateCard ( $cardnumber ) 

{ 

   $cardnumber = preg_replace ( " /\D|\s/ " , "" , $cardnumber ) ; # strip any non-digits 

   $cardlength = strlen ( $cardnumber ) ;

   if ( $cardlength != 0 ) 

   { 

     $parity = $cardlength % 2 ;

     $sum = 0 ;

     for ( $i = 0 ; $i < $cardlength ; $i ++ ) 

     { 

       $digit = $cardnumber [ $i ] ;

       if ( $i % 2 == $parity ) $digit = $digit * 2 ;

         if ( $digit > 9 ) $digit = $digit - 9 ;

           $sum = $sum + $digit ;

     } 

     $valid = ( $sum % 10 == 0 ) ;

     return $valid ;

   } 

   return false ;

}