<?
//------------------------
// PHP内置字符串函数实现
//------------------------

//字符串长度
function strlen ($str)
{
        if ($str == '' ) return 0;
        $count =  0;
        while (1){
                if ( $str[$count] != NULL){
                         $count++;
                        continue;
                }else{
                        break;
                }
        }
        return $count;
}

//截取子串
function substr($str, $start,  $length=NULL)
{
        if ($str== '' || $start>strlen($str )) return;
        if (($length!=NULL) && ( $start>0) && ($length> strlen($str)-$start)) return;
        if (( $length!=NULL) && ($start< 0) && ($length>strlen($str )+$start)) return;
        if ($length ==  NULL) $length = (strlen($str ) - $start);
        
        if ($start <  0){
                for ($i=(strlen( $str)+$start); $i<(strlen ($str)+$start+$length ); $i++) {
                        $substr .=  $str[$i];
                }
        }
        if ($length  > 0){
                for ($i= $start; $i<($start+$length ); $i++) {
                        $substr  .= $str[$i];
                }
        }
        if ( $length < 0){
                for ($i =$start; $i<(strlen( $str)+$length); $i++) {
                        $substr .= $str[$i ];
                }
        }
        return $substr;
}

//字符串翻转
function strrev($str)
{
        if ($str == '') return 0 ;
        for ($i=(strlen($str)- 1); $i>=0; $i --){
                $rev_str .= $str[$i ];
        }
        return $rev_str;
}

//字符串比较
function strcmp($s1,  $s2)
{
        if (strlen($s1) <  strlen($s2)) return -1 ;
        if (strlen($s1) > strlen( $s2)) return 1;
        for ($i =0; $i<strlen($s1 ); $i++){
                if ($s1[ $i] == $s2[$i]){
                        continue;
                }else{
                        return false;
                }
        }
        return  0;
}

//查找字符串
function  strstr($str, $substr)
{
         $m = strlen($str);
        $n = strlen($substr );
        if ($m < $n) return false ;
        for ($i=0; $i <=($m-$n+1); $i ++){
                $sub = substr( $str, $i, $n);
                if ( strcmp($sub, $substr) ==  0)  return $i;
        }
        return false ;
}

//字符串替换
function str_replace($substr , $newsubstr, $str)
{
         $m = strlen($str);
        $n = strlen($substr );
        $x = strlen($newsubstr );
        if (strchr($str, $substr ) == false) return false;
        for ( $i=0; $i<=($m- $n+1); $i++){
                 $i = strchr($str,  $substr);
                $str = str_delete ($str, $i, $n);
                $str = str_insert($str,  $i, $newstr);
        }
        return $str ;
}
?>

<?php
//--------------------
// 自实现字符串处理函数
//--------------------

//插入一段字符串
function str_insert($str, $i , $substr)
{
        for($j=0 ; $j<$i; $j ++){
                $startstr .= $str[$j ];
        }
        for ($j=$i; $j <strlen($str); $j ++){
                $laststr .= $str[$j ];
        }
        $str = ($startstr . $substr  . $laststr);
        return $str ;
}

//删除一段字符串
function str_delete($str , $i, $j)
{
        for ( $c=0; $c<$i;  $c++){
                $startstr .= $str [$c];
        }
        for ($c=( $i+$j); $c<strlen ($str); $c++){
                $laststr  .= $str[$c];
        }
         $str = ($startstr . $laststr );
        return $str;
}

//复制字符串
function strcpy($s1, $s2 )
{
        if (strlen($s1)==NULL || !isset( $s2)) return;
        for ($i=0 ; $i<strlen($s1);  $i++){
                $s2[] = $s1 [$i];
        }
        return $s2;
}

//连接字符串
function strcat($s1 , $s2)
{
        if (!isset($s1) || !isset( $s2)) return;
        $newstr = $s1 ;
        for($i=0; $i <count($s); $i ++){
                $newstr .= $st[$i ];
        }
        return $newsstr;
}

//简单编码函数（与php_decode函数对应）
function php_encode($str)
{
        if ( $str=='' && strlen( $str)>128) return false;
        for( $i=0; $i<strlen ($str); $i++){
                 $c = ord($str[$i ]);
                if ($c>31 && $c <107) $c += 20 ;
                if ($c>106 && $c <127) $c -= 75 ;
                $word = chr($c );
                $s .= $word;
        } 
        return $s; 
}

//简单解码函数（与php_encode函数对应）
function php_decode($str)
{
        if ( $str=='' && strlen($str )>128) return false;
        for( $i=0; $i<strlen ($str); $i++){
                $c  = ord($word);
                if ( $c>106 && $c<127 ) $c = $c-20;
                if ($c>31 && $c< 107) $c = $c+75 ;
                $word = chr( $c);
                $s .= $word ;
        } 
        return $s; 
}

//简单加密函数（与php_decrypt函数对应）
function php_encrypt($str)
{
         $encrypt_key = 'abcdefghijklmnopqrstuvwxyz1234567890';
         $decrypt_key = 'ngzqtcobmuhelkpdawxfyivrsj2468021359';
        if ( strlen($str) == 0) return  false;
        for ($i=0;  $i<strlen($str); $i ++){
                for ($j=0; $j <strlen($encrypt_key); $j ++){
                        if ($str[$i] == $encrypt_key [$j]){
                                $enstr .=  $decrypt_key[$j];
                                break;
                        }
                }
        }
        return $enstr;
}

//简单解密函数（与php_encrypt函数对应）
function php_decrypt($str)
{
         $encrypt_key = 'abcdefghijklmnopqrstuvwxyz1234567890';
         $decrypt_key = 'ngzqtcobmuhelkpdawxfyivrsj2468021359';
        if ( strlen($str) == 0) return  false;
        for ($i=0;  $i<strlen($str); $i ++){
                for ($j=0; $j <strlen($decrypt_key); $j ++){
                        if ($str[$i] == $decrypt_key [$j]){
                                $enstr .=  $encrypt_key[$j];
                                break;
                        }
                }
        }
        return $enstr;
}
?>