Leon Poon wrote:
> Refer to the following line numbers:
> 01 > <?php
> 02 > // Start of PHP code - Extract values from form.
> 03 > /* Other values read */
> 04 > $n=$_POST['n'];
> 05 >
> 06 > // Pass the data from the form to lightcurve_csharp
> 07 > $command="./lightcurve_csharp $a $i $e $lomega $bomega $lambda $n";
> 08 > $result=`$command`;
> 09 >
> 10 > $form_submitted=$_POST['form_sumbitted'];
> 11 > if (isset($form_submitted)) {
> 12 > if ($form_submitted) {
> 13 > echo 'The form has been submitted<br>';
> 14 > unset($form_submitted);
> 15 > }
> 16 > } else
> 17 > echo 'The form has not been submitted<br>';
> When the user first load the page, no data was posted. So there was no
> $_POST['form_sumbitted'] available. Line 10 will cause $form_submitted to
> contain the NULL value (I think). $form_submitted will evaluate to FALSE at
> line 12. Thus it will not display any message.
> By the way, by doing line 10, $form_submitted would have been set regardless
> whether there is $_POST['form_sumbitted'], and line 11 will evaluate to TRUE
> always. Thus you will never ever see the 'form not been submitted' message.
> Anyway, when you posted for the first time, $_POST['form_sumbitted'] is
> available. The 'The form has been submitted<br>' message will be printed.
> After that, when you press Reload button on the browser, the post data will
> once again be sent from the user. (This is the behaviour of reloading a
> posted page. In Internet Explorer there should be a message dialog box
> asking the user whether to resend form data in order to refresh.) Reposting
> the data during the reload means that there will be
> $_POST['form_sumbitted'], thus once again the 'form hass been submitted'
> message.
> In order to prevent this from happening, you should do a header('Location:
> success-page.php') on a successful submit. This is so that at the redirected
> page, the user would not have resent data even if he press the Reload
> button.
> Hope this helps
> -Leon
Many thanks - at the top of the file I put in the code:
if ($_POST['submit'])
header('Location: .../submitted.php');
where further down in the form I have name="submit" for the submit button.
This goes to a new page submitted.php. The code is in fact now at
http://proteus.as.arizona.edu/~csharp/lightcurved.php .
No doubt there is still a way of writing back to the original page after
the submit button has been clicked, but I can't see an easy way, so this
will have to do for now. A work-around is to do it in frames, and write
to a frame at the bottom so that it appears to be in the same page.
Christopher Sharp
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