Validating Data in C programming

MQ · Aug 5 '06, 09:05 AM

Re: Validating Data in C programming

gurdz wrote:

Does anyone know how to perform data validation in C? I have searched
google for every possible result, and I either end up with data
validation for C++ or nothing at all. I have also searched websites
such as planet-source-code.com, but my search has been in vain.
>
Can someone please help me out. Or at least, point me in the right
direction?
>
Thank you very much. :)

Data validation is a generic programming technique that is language
independant. It is just the process of checking that data input to
your program is within the range of expected values, etc. If you are
expecting a number between 1 and 10, check that it is a number between
1 and 10 before using it. What is so hard about that? Unless I am not
understanding your question...

**Flash Gordon** · Aug 5 '06, 10:05 AM

Re: Validating Data in C programming

gurdz wrote:

Does anyone know how to perform data validation in C?

Yes, you look at the data and see if it matches your validation rules.

I have searched
google for every possible result, and I either end up with data
validation for C++ or nothing at all. I have also searched websites
such as planet-source-code.com, but my search has been in vain.
>
Can someone please help me out. Or at least, point me in the right
direction?

It really depends on what the data you are trying to validate is, what
the rules are, and where the data is coming from. There is no one size
fits all solution.
--
Flash Gordon
Still sigless on this computer.

**Richard Heathfield** · Aug 5 '06, 10:15 AM

Re: Validating Data in C programming

Flash Gordon said:

<snip>

>
It really depends on what the data you are trying to validate is, what
the rules are, and where the data is coming from. There is no one size
fits all solution.

Yes, there is.

The following fragment is taken from the source code used by a major UK
bank, the identity of which will remain anonymous (to protect the guilty).
It was spotted during Y2K work in the late 1990s:

if(d != 6)
{
d = 6;
}

Viola! All numbers are 6, even if they aren't. QED.

How we laughed! We laughed and laughed and laughed, until we stopped.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

**lovecreatesbeauty** · Aug 5 '06, 10:45 AM

Re: Validating Data in C programming

Richard Heathfield wrote:

The following fragment is taken from the source code used by a major UK
bank, the identity of which will remain anonymous (to protect the guilty).
It was spotted during Y2K work in the late 1990s:
>
if(d != 6)
{
d = 6;
}
>
Viola! All numbers are 6, even if they aren't. QED.
>
How we laughed! We laughed and laughed and laughed, until we stopped.

It is possible that there are occasions for using it.

MQ · Aug 5 '06, 10:45 AM

Re: Validating Data in C programming

Richard Heathfield wrote:

The following fragment is taken from the source code used by a major UK
bank, the identity of which will remain anonymous (to protect the guilty).
It was spotted during Y2K work in the late 1990s:
>
if(d != 6)
{
d = 6;
}
>

I don't think that it is any secret that banks have their own brand of
logic, that seems to err in their favour

**Andrew Poelstra** · Aug 5 '06, 04:35 PM

Re: Validating Data in C programming

On 2006-08-05, lovecreatesbeau ty <lovecreatesbea uty@gmail.comwr ote:

>
Richard Heathfield wrote:

>The following fragment is taken from the source code used by a major UK
>bank, the identity of which will remain anonymous (to protect the guilty).
>It was spotted during Y2K work in the late 1990s:
>>
>if(d != 6)
>{
> d = 6;
>}
>>
>Viola! All numbers are 6, even if they aren't. QED.
>>
>How we laughed! We laughed and laughed and laughed, until we stopped.

>
It is possible that there are occasions for using it.
>

....where typing `d = 6' or even just `6' wouldn't suffice?

--
Andrew Poelstra <http://www.wpsoftware. net/projects>
To reach me by email, use `apoelstra' at the above domain.
"Do BOTH ends of the cable need to be plugged in?" -Anon.

**Malcolm** · Aug 5 '06, 05:05 PM

Re: Validating Data in C programming

"Andrew Poelstra" <apoelstra@fals e.sitewrote

On 2006-08-05, lovecreatesbeau ty <lovecreatesbea uty@gmail.comwr ote:

>>
>Richard Heathfield wrote:

>>The following fragment is taken from the source code used by a major UK
>>bank, the identity of which will remain anonymous (to protect the
>>guilty).
>>It was spotted during Y2K work in the late 1990s:
>>>
>>if(d != 6)
>>{
>> d = 6;
>>}
>>>
>>Viola! All numbers are 6, even if they aren't. QED.
>>>
>>How we laughed! We laughed and laughed and laughed, until we stopped.

>>
>It is possible that there are occasions for using it.
>>

>
...where typing `d = 6' or even just `6' wouldn't suffice?
>

if(d != 6)
{
fprintf(stderr, "somethign fishy here\n");
d = 6;
}

if(d != 6)
{
// fprintf(stderr, "somethign fishy here\n");
d = 6;
}

Three months later, another compiler
Warning, non-standard comment line 3456

if((d != 6)
{
d = 6;
}

--

https://www.personal.leeds.ac.uk/~bgy1mm

freeware games to download.

**Al Balmer** · Aug 5 '06, 05:35 PM

Re: Validating Data in C programming

On Sat, 05 Aug 2006 10:18:58 +0000, Richard Heathfield
<invalid@invali d.invalidwrote:

>Flash Gordon said:
>
><snip>

>>
>It really depends on what the data you are trying to validate is, what
>the rules are, and where the data is coming from. There is no one size
>fits all solution.

>
>Yes, there is.
>
>The following fragment is taken from the source code used by a major UK
>bank, the identity of which will remain anonymous (to protect the guilty).
>It was spotted during Y2K work in the late 1990s:
>
>if(d != 6)
>{
d = 6;
>}
>
>Viola! All numbers are 6, even if they aren't. QED.
>
>How we laughed! We laughed and laughed and laughed, until we stopped.

<gLooks like a left-over debug statement. A place to set a
breakpoint.

--
Al Balmer
Sun City, AZ

**Eric Sosman** · Aug 5 '06, 06:45 PM

Re: Validating Data in C programming

Andrew Poelstra wrote:

On 2006-08-05, lovecreatesbeau ty <lovecreatesbea uty@gmail.comwr ote:
>

>>Richard Heathfield wrote:
>>

>>>The following fragment is taken from the source code used by a major UK
>>>bank, the identity of which will remain anonymous (to protect the guilty).
>>>It was spotted during Y2K work in the late 1990s:
>>>
>>>if(d != 6)
>>>{
>> d = 6;
>>>}
>>>
>>>Viola! All numbers are 6, even if they aren't. QED.
>>>
>>>How we laughed! We laughed and laughed and laughed, until we stopped.

>>
>>It is possible that there are occasions for using it.
>>

>
>
...where typing `d = 6' or even just `6' wouldn't suffice?

It's an optimization. On a virtual memory system, it avoids
setting the "dirty" bit for a memory page unnecessarily, thereby
avoiding the (potential) expense of a page-out operation later,
or at least not incurring the expense for no good purpose.

(Hmmm: That variable name, `d'. Was the author, by any
chance, named Reginald?)

--
Eric Sosman
esosman@acm-dot-org.invalid

**Richard Heathfield** · Aug 5 '06, 06:45 PM

Re: Validating Data in C programming

Eric Sosman said:

<snip>

>
It's an optimization. On a virtual memory system, it avoids
setting the "dirty" bit for a memory page unnecessarily, thereby
avoiding the (potential) expense of a page-out operation later,
or at least not incurring the expense for no good purpose.
>
(Hmmm: That variable name, `d'. Was the author, by any
chance, named Reginald?)

I don't think it would be fair to reveal the source of the source, so to
speak.

Your optimisation explanation is ingenious, but my recollection of the code
base leaves me somewhat unconvinced that it is a correct explanation of the
motivation for this particular line.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999

http://www.cpax.org.uk

email: rjh at above domain (but drop the www, obviously)

**Eric Sosman** · Aug 5 '06, 07:05 PM

Re: Validating Data in C programming

Richard Heathfield wrote:

Eric Sosman said:
>
<snip>
>

> It's an optimization. On a virtual memory system, it avoids
>>setting the "dirty" bit for a memory page unnecessarily, thereby
>>avoiding the (potential) expense of a page-out operation later,
>>or at least not incurring the expense for no good purpose.
>>
> (Hmmm: That variable name, `d'. Was the author, by any
>>chance, named Reginald?)

>
>
I don't think it would be fair to reveal the source of the source, so to
speak.
>
Your optimisation explanation is ingenious, but my recollection of the code
base leaves me somewhat unconvinced that it is a correct explanation of the
motivation for this particular line.

Must have been good old Reginald K. Denktash, then.

--
Eric Sosman
esosman@acm-dot-org.invalid

**gurdz** · Aug 6 '06, 03:25 AM

Re: Validating Data in C programming

Well, I'm sorry if I got each and every person confused about data
validation, but actually, this question was raised because of my Data
Structures and Algorithms lecturer. She didn't teach us nuts about
validation, and she comes to class saying that we all have to do "data
validation for input".

I hope you all don't mind giving me some advice on this. I usually
don't ask people for this sort of help for assignments, as some see it
as unfair, however, I am totally lost on this subject.

Thanks once again,
kind regards,
Gurdip

**gurdz** · Aug 6 '06, 03:25 AM

Re: Validating Data in C programming

Well, I'm sorry if I got each and every person confused about data
validation, but actually, this question was raised because of my Data
Structures and Algorithms lecturer. She didn't teach us nuts about
validation, and she comes to class saying that we all have to do "data
validation for input".

I hope you all don't mind giving me some advice on this. I usually
don't ask people for this sort of help for assignments, as some see it
as unfair, however, I am totally lost on this subject.

Thanks once again,
kind regards,
Gurdip

**Gordon Burditt** · Aug 6 '06, 05:15 AM

Re: Validating Data in C programming

>Well, I'm sorry if I got each and every person confused about data

>validation, but actually, this question was raised because of my Data
>Structures and Algorithms lecturer. She didn't teach us nuts about
>validation, and she comes to class saying that we all have to do "data
>validation for input".

Consider, for example, an input of a bet amount for a roulette game.
Chips cost $1 each.

If the bet is a valid number (e.g. contains no alphabetic characters),
and the bet is greater than zero and the bet is less than or equal
to the house limit and the bet is an integer and the bet is less
than or equal to the player's bank balance, then the bet amount is
valid.

Reminder: a great way to cheat at poorly-written gambling programs
is to bet a negative amount, using the house advantage against it,
then try to "lose".

Consider, for example, an input which is a telephone number. How
do you validate it?

Hint: isdigit(buffer[0]) returns 0 if the first character in buffer[]
is not a digit, and nonzero if it is.

Try 1: A valid telephone number consists only of digits.
User inputs: 1-800-555-1212
Try 2: A valid telephone number consists only of digits after removing
the characters -, (, ), and blanks.
User inputs: 1-800-555
Try 3: A valid telephone number consists of 10 digits after removing
the characters -, (, ), and blanks.
User inputs: 18005551212
Try 4: A valid telephone number consists of 10 digits after removing
the characters -, (, ), and blanks. If the input is 11 digits and
the first digit is a 1, remove it.
User inputs +44 1277 655112
Try 5: A valid USA telephone number consists of 10 digits after removing
the characters -, (, ), blanks, and the prefix 1 or 011, if present.
We don't care about the rest of the world.
User inputs: 18195551212
Try 6: A valid USA telephone number consists of 10 digits after removing
the characters -, (, ), blanks, and the prefix 1 or 011, if present.
Reject input whose first 3 digits after substitutions is a Canadian
or Mexican area code. Note that this code requires modification when a
new non-USA area code is assigned. We don't care about the rest of the world.
User inputs: 12145551212 Extension 234
<Programmer shoots User>

Validating Data in C programming

Validating Data in C programming

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