Implementing pageup pagedown feature using C language

Dear all, 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.With in the given view area if the whole message does not fit,we need to provide the ability for users to scroll through the entire message using pageup/pagedown or key up and key down.In our case we have the whole contents to be displayed stored in a buffer.I am giving below one implementation I have tried:

Note:We are using only pure C code and dont have active x controls like tabs or pageup/down buttons as in .NET or VC++.

#include #include "string.h"

void pageup(); void pagedown(); static int pagecounter=0; /*bytes per page calculated by trial and error considering the viewable area in my device*/ int bytesperpage=161; int numpages=0; int contentremaining=0; char* customstringcopy=NULL; char arr[161]={0}; int main(int argc, char *argv[]) { int totlen=0; int pagenum=0;

char* customstring=NULL;

char* data="Bloodshed Dev-C++ is a full-featured Integrated Development Environment (IDE) for the C/C++ programming language. It uses Mingw port of GCC (GNU Compiler Collec."; char* stringdata="Bloodshed Dev-C++ is a full-featured Integrated Development Environment (IDE) for the C/C++ programming language. It uses Mingw port of GCC (GNU Compiler Collection) as it's compiler. Dev- C++ can also be used in combination with Cygwin or any other GCC based compiler."; char* stringdata1="the #bloodshed channel has recently been created on the Undernet IRC server. I will be please to talk with you there so feel free to join :) If you want have an IRC client you can get one for Windows at and for Linux at"; char* stringdata2="You can subscribe to the Dev-C++ mailing list (for asking and answering questions on Dev-C++ and C/C++ programming) by clicking here and filling out the subscribe form there.";

totlen=strlen(stringdata)+strlen(stringdata)+strlen(stringdata2); printf("total length is %d\n",totlen); printf("length of data is %d\n",strlen(data) ); customstring=(char*)(malloc)(totlen+4); customstringcopy=customstring; memset(customstring,0,totlen+4);

memcpy(customstring,stringdata,strlen(stringdata)); customstring=customstring+strlen(stringdata); customstring[0]='\n'; customstring++; /*printf("%s\n",stringdata); printf("%s\n",customstringcopy);*/

/*customstring[0]='\n'; customstring++;*/

memcpy(customstring,stringdata1,strlen(stringdata1)); customstring=customstring+strlen(stringdata1); customstring[0]='\n'; customstring++; /*printf("%s\n",stringdata1); printf("%s\n",customstringcopy);*/

memcpy(customstring,stringdata2,strlen(stringdata2)); customstring=customstring+strlen(stringdata2); customstring[0]='\n'; customstring++; /* printf("%s\n",stringdata2);*/ printf("%s\n",customstringcopy);

numpages=totlen/bytesperpage; printf("total number of pages is %d\n",numpages); contentremaining=(totlen)%(bytesperpage); if(contentremaining > 0) { numpages=numpages+1;

} printf("total number of pages is %d\n",numpages); for(pagenum=0;pagenum0;pagenum--) { pagedown(); } system("PAUSE"); return EXIT_SUCCESS; }

void pageup() {

if(pagecounter1) { pagecounter--; printf("pagecounter value is %d \n",pagecounter); customstringcopy=customstringcopy-(bytesperpage); memcpy(arr,customstringcopy,161); printf("%s\n\n",arr); }

} /* if(pagecounter>0) {

customstringcopy=customstringcopy- bytesperpage; memcpy(arr,customstringcopy,161); printf("%s\n\n",arr);

} */


Incase you find bugs in above code please let me know ways to fix it.

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.

Note:I am looking for only C code and not C#,JAVA,.NET,VC++

Looking farward for all your replies and advanced thanks for the same, Regards, s.subbarayan

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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.
Reply to
Malcolm McLean

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 #include "string.h"

Do: #include #include #include

[Always use angle brackets for standard libraries] [malloc() is defined in ] Don't: totlen=strlen(stringdata)+strlen(stringdata)+strlen(stringdata2);

Do: totlen = strlen(stringdata) + strlen(stringdata1) + strlen(stringdata2);

[Silly mistake: we all make them] Don't: numpages=totlen/bytesperpage; printf("total number of pages is %d\n",numpages); contentremaining=(totlen)%(bytesperpage); if(contentremaining > 0) { numpages=numpages+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
Reply to
Andrew Smallshaw

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