PHP substr_replace 替换字符串指定位置字符

<?php
substr_replace('abcd', 'x', 0, -4); //xabcd
?>

Same as:
<?php
substr_replace('abcd','x',0,0); //xabcd
?>

<?php
substr_replace('abcd', 'x', 1, -3); //axbcd
?>

Same as:
<?php
substr_replace('abcd', 'x', 1, 0); //axbcd
?>

//strlen
//int strlen ( string $string )

$str = '123456';
echo strlen($str); // 6

$str = ' ab cd www.111cn.net';
echo strlen($str); // 20

$ch ='中国';

echo strlen($ch);//4

function utf8_strlen($str)
    {
    $count = 0;

    for($i = 0; $i < strlen($str); $i++)
        {
        $value = ord($str[$i]);
        if($value > 127)
            {
            if($value >= 192 && $value <= 223)
                $i++;
            elseif($value >= 224 && $value <= 239)
                $i = $i + 2;
            elseif($value >= 240 && $value <= 247)
                $i = $i + 3;
            else
                die('Not a UTF-8 compatible string');
            }
      
        $count++;
        }
  
    return $count;
}

$timestamp = time();
function open($file,$type=''){
        global $fromurl,$referer;
        $cachename=$file;
                if($type){
                        $file='/'.$type.'/'.$file;
                }else{
                        $file=$file;
                }
                        if($open=file($file)){
                                        $count=count($open);
                                        for($i=0;$i<$count;$i++){
                                                $theget.=$open[$i];
                                        }
                                }else{
                                        die('无法连接源站网络，请刷新');
                                }
        return $theget;
}

function cut($file,$from,$end){
        $message=explode($from,$file);
        $message=explode($end,$message[1]);
return        $message[0];
}

function curl($openurl)
{
 global $isfun;
 if($isfun=="curl"){
 $ch = curl_init($openurl);
 curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
 curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
 $file = curl_exec($ch);
 curl_close($ch);
 }
 elseif($isfun=="fopen"){
  $file=open($openurl);
 }
 else{ echo "<script>alert('你的空间不支持本程序，谢谢使用');window.close();</script>";}
 return $file;
}

function isfun($funName)
 {
        return (false !== function_exists($funName))?YES:NO;
 }
?>