Implementing pageup pagedown feature using C language

**Malcolm McLean** · Oct 28 '08, 08:45 PM

Re: Implementing pageup pagedown feature using C language

"ssubbaraya n" <ssubba@gmail.c omwrote in message

I am in the process of implementing pageup/pagedown feature in our
consumer electronics project.The idea is to provide feature to the
customers to that similar to viewing a single sms message in a mobile
device.
>

You can speed this up a lot.

Hold the message in a single, contiguousm, NUL-terminated buffer (i.e. a big
string).
Then provide a function.

int getNpages(char *message, int width, int height)

Basically you count one column for a character, one line for a newline. Then
you divide the answer by the number of lines per page.

Now we have

void printpage(FILE *fp, char *message, int page)

it is essentially the same function as the previous one, counting columns
and lines, except that when you get to the page you want, you start calling
putchar(). No temporary buffers are required.

--
Free games and programming goodies.

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

**Andrew Smallshaw** · Oct 29 '08, 01:45 PM

Re: Implementing pageup pagedown feature using C language

On 2008-10-28, ssubbarayan <ssubba@gmail.c omwrote:

>
I believe there are much better ways then the one I have tried here.It
would be helpful if some one could provide me some sample code for
similar features you would have come across in your product or some
sample links which shows me sample code on how to implement such a
feature.

How did you design this code? In a sense that is a rhetorical
question because I already know how you wrote it - you opened up
your text editor and started typing, right? It shows in the code.
If it was me and I wanted to have some pride in my work I would
delete it now and start over. I'd probably end up saving time in
the long run because this code simply isn't maintainable.

I suspect you have already spent hours bashing this code into
shape. Next time, invest a little time in design first. Turn
off your computer, find a pad of paper, a pencil and a rubber and
don't go back to your computer until you know how every aspect of
your code is going to work. Your code will go together far more
quickly, and be much tidier and more compact to boot.

Returning to your code, reading between the lines it appears that
arr is supposed to represent a memory-mapped display device - this
isn't mentioned anywhere and that is one of the first things you
should specify in an early stage of designing your code. Similarly
I spent some time looking around for where you receive input from
the user, before realising that you weren't doing this, but
running through a predefined test sequence; again something that
should have been mentioned. I also take it that all those printfs
littering your code are debug code to try and get your code
working - they shouldn't be needed for something like this.

I _really_ doubt arr should be 161 characters long and your trial
and error comment does little to inspire confidence. 160 is much
more likely, quite possibly on a 40x4 matrix. If that's the case
then what about line breaks - presumably we need to wrap at word
boundaries which you aren't doing here. I can understand why you
got 161 - you need one for the trailing NULL character to treat
the display buffer as a string. Big mistake - it is a character
array, not a string, and if you start writing to arr[161] that
may well be some special function register associated with the
display.

Looking through your code in a little more detail, a few more
specific issues do come to mind.

Don't:
#include <stdio.h>
#include "string.h"

Do:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

[Always use angle brackets for standard libraries]
[malloc() is defined in <stdlib.h>]

Don't:
totlen=strlen(s tringdata)+strl en(stringdata)+ strlen(stringda ta2);

Do:
totlen = strlen(stringda ta) + strlen(stringda ta1) + strlen(stringda ta2);

[Silly mistake: we all make them]

Don't:
numpages=totlen/bytesperpage;
printf("total number of pages is %d\n",numpages) ;
contentremainin g=(totlen)%(byt esperpage);
if(contentremai ning 0)
{
numpages=numpag es+1;

}
printf("total number of pages is %d\n",numpages) ;

Do:
numpages = (totlen + (bytesperpage - 1)) / bytesperpage;
printf("total number of pages is %d\n", numpages);

[More compact and faster]
[This is a standard pattern whenever you need to round a division up]
[Test it with a pen and paper to prove to yourself it works]

--
Andrew Smallshaw
andrews@sdf.lon estar.org

Implementing pageup pagedown feature using C language

Implementing pageup pagedown feature using C language

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