html form error handling

[chucklarge]

Hi,
I want to know the best way to build a form error handling scheme. If there is an error in filling out a form, either blank field, invalid email, etc, i want to highlight those areas on the form that have an error and not be directed to an error page listing the errors. All correct info would be populated back into the field and invalid info unset.

I would like this to be scheme to not be specific form dependent, meaning i can use it for any form without much modification. I know that javascript could be used, but i want a php solution.

What are anyone's ideas?

chuck

[Installer]

Here's a script you might be able to work from:

$input = array('name' => '', 'id' => '');
if (!isset($_POST['submit'])) {
    echo form($input);
} else {
    $error = false;
    if (!valid_name($_POST['name'])) {
        $error = true;
        $name  = 'error';
    } else {
        $name = $_POST['name'];
    }
    if (!valid_id($_POST['id'])) {
        $error = true;
        $id    = 'error';
    } else {
        $id = $_POST['id'];
    }
    if ($error) {
        $input['name'] = $name;
        $input['id']   = $id;
        echo form($input);
    } else {
        echo 'Your input is accepted.<br />';
        echo $name . '<br />';
        echo $id   . '<br />';
    }
}

function form($array)
{
    $ret  = '<form action="' . $_SERVER['PHP_SELF'] . 
            '" method="post">';
    $ret .= input_line($array['name'], 'name', 'Name');
    $ret .= '<br />';
    $ret .= input_line($array['id'], 'id', 'ID #');
    $ret .= '<br /><input type="submit" name="submit" ' .
            'value="submit" />';
    $ret .= '</form>';
    return $ret;
}

function input_line($data, $key, $label) 
{
    if ($data == 'error') {
        $color = 'red';
        $value = '';
    } else {
        $color = 'black';
        $value = $data;
    }
    $ret  = '<font color="' . $color . '">' . $label . 
            ': </font>';    

    $ret .= '<input type="text" name="' . $key . 
            '" value="' . $value . '" />';
    return $ret;
}

function valid_name($name) {
    if (strlen($name) < 5) {
        return false;
    } else {
        return true;
    }
}

function valid_id($id) {
    if (!is_numeric($id)) {
        return false;
    } else {
        return true;
    }
}

It's not perfect, of course; the logic could be tightened, styles could be used, it might be better as a class because of function/variable interdependence, etc. But maybe it will help.

There's a good article on form error handling here (although I'm not fond of the coding style 🙂 ).