if($res !== false){
    echo "未定义通过<br>";
}else{
    echo "未定义不通过<br>";
}

$res = 0;
if($res !== false){
    echo "0数字通过<br>";
}else{
    echo "0数字不通过<br>";
}

$res = "0";
if($res !== false){
    echo "0字符串通过<br>";
}else{
    echo "0字符串不通过<br>";
}

$res = NULL;
if($res !== false){
    echo "NULL通过<br>";
}else{
    echo "NULL不通过<br>";
}

$res = "";
if($res !== false){
    echo "空字符串通过<br>";
}else{
    echo "空字符串不通过<br>";
}

$res = array();
if($res !== false){
    echo "array()通过<br>";
}else{
    echo "array()不通过<br>";
}

$res = FALSE;
if($res !== false){
    echo "FALSE通过<br>";
}else{
    echo "FALSE不通过<br>";
}

$res = TRUE;
if($res !== false){
    echo "TRUE通过<br>";
}else{
    echo "TRUE不通过<br>";
}

$res = 1;
if($res !== false){
    echo "数字1通过<br>";
}else{
    echo "数字1不通过<br>";
}