Set_select（）不适用于CodeIgniter

I have a select box in my form and when I hit submit the form goes through validation and if an error happens, return all the value. This work expect for my select box, I have use the set_select but it doesnt work data comes in data base

<select name="leave_category_id" class="form-control" onchange="check_leave_category(this.value)" required  >
    <option value="" >Select Leave Category...</option>
    <?php foreach ($all_leave_category as $v_category) :

        ?>
        <option value="<?php echo $v_category->leave_category_id ?>" >
            <?php echo set_select('leave_category_id',$cat); ?>
            <?php echo $v_category->category ?>  </option>
    <?php endforeach;

    ?>
</select>

The set_select() function prints out the selected="selected" attribute in the <option> element where appropriate. But your code is as follows:

<option value="<?php echo $v_category->leave_category_id ?>" >
                                                             ^
                                    closing the tag   -->    |
    <?php echo set_select('leave_category_id',$cat); ?>
    <?php echo $v_category->category ?>  
</option>

So when you look at the html, it will look something like this:

<option value="123">selected="selected" Category Name</option>

Got it? Your selected attribute is placed outside the tag. I guess you'll be able to fix it now ;)