字符串与ascii的转换

 字符串中只能包含字符，特殊符号不行。

//字符串转化为ascii

function  str2asc( $str )

{

     $num = '' ;

     while ( strlen ( $str ) != 0 )

    {

         $a = substr ( $str , 0 , 1 );

         $num .= ord ( $a );

         $str = substr ( $str , 1 , strlen ( $str ));

    }

     return   $num ;

}

//ascii转化为字符串

function  asc2str( $num )

{

     $num = ( string ) $num ;

     $str = '' ;

     while ( strlen ( $num ) != 0 )

    {

         $a = (int) substr ( $num , 0 , 1 );

         if ( $a > 2 )

        {

             $b = (int) substr ( $num , 0 , 2 );

             $num = substr ( $num , 2 , strlen ( $num ));

        } else

        {

             $b = (int) substr ( $num , 0 , 3 );

             $num = substr ( $num , 3 , strlen ( $num ));

        }

         $str .= chr ( $b );

    }

     return   $str ;

}

示例:

echo str2asc( 'sfdsl ');

echo  ' <br > ';

echo asc2str(str2asc( 'sfdsl '));

---------------------

115102100115108

sfdsl 

注：调用asc2str( '123456 ') 不能asc2str(123456) ，也就是要将123456转化为字符串。