How to convert string to binary in php

/**
    * 将字符串转换成二进制
    * @param type $str
    * @return type
    */
    function StrToBin($str){
        //1.列出每个字符
        $arr = preg_split(&#39;/(?<!^)(?!$)/u&#39;, $str);
        //2.unpack字符
        foreach($arr as &$v){
            $temp = unpack(&#39;H*&#39;, $v);
            $v = base_convert($temp[1], 16, 2);
            unset($temp);
        }
        return join(&#39; &#39;,$arr);
    }
    /**
    * 将二进制转换成字符串
    * @param type $str
    * @return type
    */
    function BinToStr($str){
        $arr = explode(&#39; &#39;, $str);
        foreach($arr as &$v){
            $v = pack("H".strlen(base_convert($v, 2, 16)), base_convert($v, 2, 16));
        }
        return join(&#39;&#39;, $arr);
    }