[help-cgicc] Re: help-cgicc Digest, Vol 34, Issue 2

[Steven King]

Hi Juju,

This program was causing a segmentation fault at the isEmpty() line when 
I ran it from the command line.

It is caused by trying to call isEmpty() on an empty object. If the 
call  "fvalue1 != (*formData).end()" fails,
this means that the iterator is pointing to nothing so you cant call 
methods on it.

To fix the tutorial, simply change the order on the if and let 
precedence take care of checking for an empty iterator, that is:
Change:

if( !fvalue1->isEmpty() && fvalue1 != (*formData).end())

to:

if((fvalue1 != (*formData).end()) && !fvalue1->isEmpty())

Also, the output HTML is incorrect -> you need to remove the second html() call.

Cheers,

Steve King


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> Today's Topics:
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>   1. problems with forms submitted via http POST
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Sat, 29 Jul 2006 15:54:22 +0200
> From: address@hidden
> Subject: [help-cgicc] problems with forms submitted via http POST
> To: address@hidden
> Message-ID: <address@hidden>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
>
> my cgi program and a tutorial cgicc program both crash when
> called with the http "POST" method and with some ?key=value
> added to the url.
>
> The program crash is in the call to isEmpty() in a context like here:
> //-------------------------------
> form_iterator fvalue1 = formData.getElement("value1");
> if( !fvalue1->isEmpty() && fvalue1 != (*formData).end())
> {
> cout << "Value1: " << **fvalue1 << endl;
> }
> //-------------------------------
>
> this problem only shows when all of the 3 following conditions concur:
> a) the cgi program receives data via the POST method
> b) the url has key/value pairs added as in the GET method
> c) there's a call to FormEntry::isEmpty() or FormEntry::length
>
> - if instead of a) i use http GET, then it works fine, and i can even
> use code
> like the above to retrieve the http get vars.
> - if instead of b) there are no GET-type vars at the end of the url, a
> POST request
> is processed just fine. However, it seems that any cgi program used with
> http post
> shows this problem if the user just adds ?somekey=somevalue to the url.
> - if instead of c) i don't use FormEntry, it works fine even if i use
> post with ?key=value
> added to the url. i could even parse these manually from the query
> string (where they
> do get transferred).
>
> if you want to reproduce this problem, just compile the example code from
> http://yolinux.com/TUTORIALS/LinuxTutorialC++CGI.html
> and call it with "POST" method AND adding any ?key=value to the url.
>
> is this a bug or  did i overlook something?
>
> Cheers,
> Juju
>
>
>
>
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> End of help-cgicc Digest, Vol 34, Issue 2
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