如何编写一个函数来检查变量是否已定义并且是一个数字？

Question

In the past when I needed to check if a variable was set and also a number, I would do:

if( isset($_GET['var']) && is_numeric($_GET['var']) )

But I think that's kind of ugly, especially when I need to check a bunch of variables in the same if statement, so I made a function:

function setAndNum($var)
{
    if(isset($var) && is_numeric($var))
        return 1;
    else
        return 0;
}

The problem is that when I pass an undefined variable to the function, like this (supposing the variable in the GET array is undefined):

if( setAndNum($_GET['var']) )

I get the php error:

Notice: Undefined index: ...

So the whole purpose of the function is basically defeated (or half the purpose, at least ;) ).

One thing that confuses me is how the isset() function works, and why I can pass an undefined variable to it but not to my own function?

Is it possible to make my setAndNum() function work?

Answer 1

Your problem is with $_GET being an array. When you pass $_GET['var'] to your function, this array value is already looked up and used as an argument to the function. Therefore you cannot effectively check the presence of 'var' in $_GET from within this function. You could rewrite it a bit to make it work for array values, something like this:

function setAndNum($key, $array)
{
    if(array_key_exists($key, $array) && is_numeric($array[$key]))
        return 1;
    else
        return 0;
}

Then call it like this:

if( setAndNum('var', $_GET) )