我想使用我自己的函数来检查字符串的每个字符，我使用的是UTF8，我不想使用str_replace或preg_match，但我想知道为什么它不起作用。

`
function GarderCaractereSimple($chaineIn)
{
//Garde seulement les lettres et les chiffres
//transforme les accents en caractères simple

$TabCarSimple = array('a'=>'a','b'=>'b','c'=>'c','d'=>'d','e'=>'e','f'=>'f','g'=>'g','h'=>'h','i'=>'i','j'=>'j','k'=>'k','l'=>'l','m'=>'m','n'=>'n','o'=>'o','p'=>'p','q'=>'q','r'=>'r','s'=>'s','t'=>'t','u'=>'u','v'=>'v','w'=>'w','x'=>'x','y'=>'y','z'=>'z','A'=>'A','B'=>'B','C'=>'C','D'=>'D','E'=>'E','F'=>'F','G'=>'G','H'=>'H','I'=>'I','J'=>'J','K'=>'K','L'=>'L','M'=>'M','N'=>'N','O'=>'O','P'=>'P','Q'=>'Q','R'=>'R','S'=>'S','T'=>'T','U'=>'U','V'=>'V','W'=>'W','X'=>'X','Y'=>'Y','Z'=>'Z','0'=>'0','1'=>'1','2'=>'2','3'=>'3','4'=>'4','5'=>'5','6'=>'6','7'=>'7','8'=>'8','9'=>'9','é'=>'e','è'=>'e','à'=>'a','ç'=>'c','ù'=>'u','ê'=>'e','ï'=>'i','ë'=>'e','ô'=>'o','ö'=>'o','_'=>'_','-'=>'-');

$length = strlen($chaineIn);
$chaineOut = "";

for($i=0; $i<$length; $i++)
{
    //if(in_array($chaineIn[$i],$TabCarSimple))  //same problem
    if(isset( $TabCarSimple[$chaineIn[$i]] ))
    $chaineOut .= $chaineIn[$i];
}

return $chaineOut;
}

$test ="tést";
echo GarderCaractereSimple($test);
`

我想查找结果test，但结果为tst
我在我的服务器和一个虚拟的PHP引擎上试了试，我也有同样的问题。
如果$chaineIn[$i]与重音字符匹配，为什么我无法正确读取$TabCarSimple[$chaineIn [$i]]？
谢谢