[SOLVED] Removing junk characters through C program

jack.sully · 03-07-2014, 02:47 AM

Hi,
I am trying to remove junk characters from a file through C program. But code is not working in desired way.No output is coming int the output_file.
Here is the code.
Junk characters in junk_file i have entered by typing numeric values >255

-bash-4.1# cat number.c
#include <stdio.h>

main()
{
FILE *fp,*fp1;
fp=fopen("junk_file","r");
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch < '0' || ch > '255') /*unget all the characters beyond the ascii bounds */
ungetc(ch,fp);
else
putc(ch,fp1); /*get rest of the characters in the output file */
}
fclose(fp);
fclose(fp1);
return(0);
}

-bash-4.1# cat junk_file
Â¦+Â¦ÃtÃ

i#include<Â¦-Â§

Any suggestions.

AnanthaP · 03-07-2014, 04:01 AM

(1) char and int can be freely mixed. BUT if you mean the numeric values 0 and 255, then you should remove quotes around them.
(2) The so called junk characters are those < 32 or those > 127.
OK

jack.sully · 03-07-2014, 04:14 AM

I have edited the code:

-bash-4.1# cat number.c
#include <stdio.h>

main()
{
FILE *fp,*fp1;
fp=fopen("junk_file","r");
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch < 32 || ch > 127) /*unget all the characters beyond the ascii bounds */
ungetc(ch,fp);
else
putc(ch,fp1); /*get rest of the characters in the output file */
}
fclose(fp);
fclose(fp1);
return(0);
}

Still the code is not working, Is their any way we can remove them form appearing in the output file.

AnanthaP · 03-08-2014, 01:08 AM

AFAIR, unget only pushes the character back to the stream and doesn't bypass it.

So try this

Quote:

{

if(ch >= 32 && ch <= 127)
putc(ch,fp1); /*put the required characters into the output file */

}

OK

s.verma · 03-08-2014, 02:31 AM

Dear jack.sully,

Quote:

Originally Posted by jack.sully

#include <stdio.h>

main()
{
FILE *fp,*fp1;
fp=fopen("junk_file","r");
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch < '0' || ch > '255') /*unget all the characters beyond the ascii bounds */
ungetc(ch,fp);
else
putc(ch,fp1); /*get rest of the characters in the output file */
}
fclose(fp);
fclose(fp1);
return(0);
}

First in your original program why you are using ungetc(int, FILE *) function. I have run and tested it, it is creating an infinite loop. It never terminates possibly because it first get character then unget it and situation repeats itself.

Try using this code

Code:

#include <stdio.h>

main()
{
FILE *fp,*fp1;
fp=fopen("junk_file","r");
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch > '0' && ch < '255') /*get desired ones */
putc(ch,fp1); /* characters in the output file */
}
fclose(fp);
fclose(fp1);
return(0);
}

Also compiling your original code gives this warning.
number.c: In function ‘main’:
number.c:12:21: warning: multi-character character constant [-Wmultichar]
if(ch < '0' || ch > '255') /*unget all the characters beyond the ascii bounds */

So I am agreed with AnanthaP that you have to remove quotes. Write 255 not '255'.

Agree with AnanthaP for replacing the code.

jack.sully · 03-09-2014, 08:42 AM

Thanks a lot guys.

Code is working now.(even though i didn't edit the code for warning)

schneidz · 03-09-2014, 10:14 AM

for shiggles heres my ascii scraper:

Code:

#include "stdio.h"
 
main(int argc, char *argv[])
{
int c;
FILE * fstream;
 
fstream = fopen(argv[1], "r");
c = fgetc(fstream);
 
while(c != EOF)
{
  if(c == 10)
   printf("%c", c);
  if((c >= 0 && c <= 9) || (c >= 11 && c <= 31))
   printf(" ");
  if(c >= 127)
   printf(" ");
  if((c >= 32 && c <= 126) && (c != 59))
   printf("%c", c);
  if(c == 59)
  {
   printf("\n");
  }
 
  c = fgetc(fstream);
}
fclose(fstream);
}

jpollard · 03-10-2014, 12:07 AM

Instead of using "printf" (which is slow) why not use fputc?

And instead of all the "ifs" used, why not a switch?

Code:

...
while (EOF != (c = fgetc(stream))) {
    switch (c) {
    case 10:
    case 32...58:
    case 60...126:
        fputc(c, stdout);
        break;

    case 59:
        fputc('\n',stdout);
        break;

    default:
        fputc(' ',stdout);
    }
}

And watch out for those "ch >255" tests -they are invalid.

ch is declared a "char", and that means it is an 8 bit signed value. There is no signed character that is 255... signed characters go from -127 to 128, so your test of "ch > 255" is never true.

Using "c" (from the example preceding mine) is declared an integer - which allows for testing for EOF (value is -1), and all values returned are then between 0 and 255...

jack.sully · 03-10-2014, 10:06 AM

-bash-4.1# cat junk_clear_new.c

#include <stdio.h>
main(int argc,char *argv[])
{
FILE *fp,*fp1;

if(argc!=2)
fprintf(stderr,"usage: %s file \n",argv[0]);

else
fp=fopen(argv[1],"r");

if(fp==NULL)
perror(argv[1]);
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch > 0 && ch < 255) /*get desired ones */
putc(ch,fp1); /* characters in the output file */
else if(ch=='\n')
printf("\n");
}
fclose(fp);
fclose(fp1);
return(0);
}
-bash-4.1#
-bash-4.1# cat try_junk
i#include<Â¦-Â§aa
tÂ¦Â¦ y u
iggÂ¦+qertÃ©
-bash-4.1#
-bash-4.1# cat output.c
i#include<-aa
t y u
igg+qert
-bash-4.1#

Mission accomplished!

jpollard · 03-10-2014, 12:13 PM

Quote:

Originally Posted by jack.sully

-bash-4.1# cat junk_clear_new.c

#include <stdio.h>
main(int argc,char *argv[])
{
FILE *fp,*fp1;

if(argc!=2)
fprintf(stderr,"usage: %s file \n",argv[0]);

else
fp=fopen(argv[1],"r");

if(fp==NULL)
perror(argv[1]);
char ch;
fp1=fopen("output.c","w");

while((ch=getc(fp))!=EOF)
{
if(ch > 0 && ch < 255) /*get desired ones */
putc(ch,fp1); /* characters in the output file */
else if(ch=='\n')
printf("\n");
}
fclose(fp);
fclose(fp1);
return(0);
}
-bash-4.1#
-bash-4.1# cat try_junk
i#include<Â¦-Â§aa
tÂ¦Â¦ y u
iggÂ¦+qertÃ©
-bash-4.1#
-bash-4.1# cat output.c
i#include<-aa
t y u
igg+qert
-bash-4.1#

Mission accomplished!

not really. You still have errors in the code...

jack.sully · 03-11-2014, 09:52 AM

yes u r very right pollard.
Problem with my code was ,after removing the junk characters from original file i was not able to preserve their empty space in the output file.

bash-4.1# cat try_junk
i#include<Â¦-Â§aa
tÂ¦Â¦ y u
iggÂ¦+qertÃ©
-bash-4.1#
-bash-4.1# cat output.c
i#include<-aa
t y u
igg+qert
-bash-4.1

Correct code is your's one

-bash-4.1# cat latest_junk_clear.c

#include <stdio.h>

main(int argc, char *argv[])
{
int ch;
FILE * fp;

fp= fopen(argv[1], "r");
ch = fgetc(fp);

while(ch != EOF)
{
if(ch == 10)
printf("%c", ch);
if((ch >= 0 && ch <= 9) || (ch >= 11 && ch <= 31))
printf(" ");
if(ch >= 127)
printf(" ");
if((ch >= 32 && ch <= 126) && (ch != 59))
printf("%c", ch);
if(ch == 59)
{
printf("\n");
}

ch = fgetc(fp);
}
fclose(fp);
}

-bash-4.1# cat try_junk
i#include<Â¦-Â§aa
tÂ¦Â¦ y u
iggÂ¦+qertÃ©
-bash-4.1#

-bash-4.1# ./latest_junk try_junk
i#include< - aa
t y u
igg +qert
-bash-4.1#

Now it's fine.

Thanks a lot