这样有意义吗？

function revStr($str)
{
    $str2 = implode(" ", array_map("strrev", explode(" ", $str)));
    $len = strlen($str);
    while ($len > 0) {
        $str2{$len - 1} = ord($str{$len - 1}) < 97 ? strtoupper($str2{$len - 1}) : strtolower($str2{$len - 1});
        $len--;
    }
    return $str2;
}

$str = 'This is an Apple on eBay';
echo revStr($str);// Siht si na Elppa no yAbe

http://segmentfault.com/q/1010000002547110/a-1020000002547831

先用$arr=explode('',$input)分割这个字符串,
然后将数组翻过来array_reverse()
然后遍历$arr
用$a=substr($arr[0],0,1)截取

if(preg_match('/^[a-z]+$/', $a)){
            echo '小写字母';
            $a=strtoupper($a)
}elseif(preg_match('/^[A-Z]+$/', $a)){
            echo '大写字母';
            $a = strtolower($a)
}

然后拼起来就完成了

我也来一个，比@util的稍微快点：）

function revStr(&$str) {
    $offset = 0;
    $isEnd = false;
    while(!$isEnd){
        $spacePos = strpos($str, ' ', $offset);
        if($spacePos === false){
            $spacePos = strlen($str);
            $isEnd = true;
        }
        
        $wordLen = $spacePos - $offset;
        $wordLenHalf = $wordLen >> 1;
        for ($j = 0; $j < $wordLenHalf; $j++) {
            $diff = 0;
            $charPos = $offset + $j;
            $charPosRev = $spacePos - $j - 1;
            $charASCII = ord($str[$charPos]);
            $charASCIIRev = ord($str[$charPosRev]);
            $diff += ($charASCII <= 90) ? -16 : 16;
            $diff += ($charASCIIRev <= 90) ? 16 : -16;
            if($diff){
                $str[$charPos] = chr($charASCIIRev + $diff);
                $str[$charPosRev] = chr($charASCII - $diff);
            }else{
                $tmp = $str[$charPos];
                $str[$charPos] = $str[$charPosRev];
                $str[$charPosRev] = $tmp;
            }
        }
        $offset += $wordLen+1;
    }
}

$str = 'This is an Apple on eBay';
revStr($str); 
echo $str;// Siht si na Elppa no yAbe

神需求，什么乱七八糟的一堆，