Why does this semicolon appear if I use jQuery serialize() on inputs with square brackets in the name?

I have the following HTML:

<input type="checkbox" id="options_1" value="options_1" name="options[]">  
<input type="checkbox" id="options_2" value="options_2" name="options[]">  
<input type="checkbox" id="options_3" value="options_3" name="options[]">  

I check the first two options and send it to the server via ajax in jQuery:

$.ajax({
    type: "POST",
    url: "myfile.php",
    data: {
        'options':$('input[name="options[]"]').serialize()
    },
    dataType: 'json',
    beforeSend: function(){
           //do some stuff
    },
    success: function(msg){
        //do some stuff
    }
});

Firebug shows me the data that has been posted:

options options%5B%5D=options_1&options%5B%5D=options_2

So far, so good.

In myfile.php I get the POST-Variable like this:

$options = $_POST['options'];

Now when I echo $options I get this:

"options[]=options_1&options;[]=options_2"

Where does this semicolon in front of the second pair of brackets come from? This is driving me crazy.

I already used utf8_decode on the POST data as well as urldecode and rawurldecode. Nothing changes. I also escaped the square brackets in the ajax call like this:

data: {
    'options':$('input[name="options\\[\\]"]').serialize()
},

That didn't help either. Any ideas anyone?

I had this exact problem, and I was only able to get it to work by using ".serializeArray()", I hope this was what you were looking for.

data: {
    'options':$('input[name="options[]"]').serializeArray()
},

For me this outputs standard string in the same format as GET requests.

I recommend to remove [] from html names, it's bad design. There can be a problem on jQuery side or PHP too. I can see no other problems in your code.

What characters are allowed in the HTML Name attribute?
What are valid values for the id attribute in HTML?

Why do you use the brackets[] and the same name for each input element? If I get you right you can serialize by a wrapping element..

<form id="options">
    <input type="checkbox" id="options_1" value="options_1" name="option1" />  
    <input type="checkbox" id="options_2" value="options_2" name="option2" />  
    <input type="checkbox" id="options_3" value="options_3" name="option3" />  
</form>

So you can serialize like

data: {
    'options':$('#options').serialize()
},

You might want to read this and try this:

data: {
        'options':$('input[name="options[]"]').replace('%5B%5D', '[]') 
    },

or this

$.param(obj, true);

The true in the $.param indicates the traditional method of serializing an object should be used. The traditional method does not use square brackets when it encounters the same parameter name.