trouble with text file reading/writing

**sbeehre** · 08-01-2006

Hi everyone

I have a text file which contains a memory dump as shown below

Code:

  Memory Address 1FD7C000 49A0 Bytes
  1FD7C000: 4D 5A 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *MZ..............*
  1FD7C010: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C020: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C030: 00 00 00 00 00 00 00 00-00 00 00 00 B8 00 00 00  *................*
  1FD7C040: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C050: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C060: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C070: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C080: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C090: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C0A0: 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00  *................*
  1FD7C0B0: 00 00 00 00 00 00 00 00-50 45 00 00 4C 01 04 00  *........PE..L...*

what i want to do is have my program read the above text file and output it into another processed file which will look like this

Code:

4D 5A 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 B8 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

and so on

A friend at my previous work gave me a hand and we came up with this

Code:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>

int main()
{

  char instring[200];
  int charpos;  // position of ":" in the string
  FILE *textfile,*outtxtfile ;

  charpos=10;
  // Process file
  textfile=fopen("dump.txt","r");
  // open the destination file
  outtxtfile=fopen("outtext.txt","w");

 // process file
  while (!feof(textfile))
	{
	fgets(instring,200,textfile); /* if ":" found in the string will confirm valid string &
				     extract it to new file */
	if(instring[10]==':')
	   {
	   // fwrite(void *buffer, size_t size, size_t num, FILE *fp);
	   fwrite(instring+charpos+2,1,30,outtxtfile);  // first lot of data ie "45  5A  00  00  00 00 00 00"
	   fwrite(instring+charpos+2+31,1,30,outtxtfile);  // second lot of 30 characters from "-" onwards
	   }
	}
  fclose(textfile);
  fclose(outtxtfile);

  return 0;
}

This program doesnt work how i would like it and returns the following

Code:

4D 5A 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *MZ.........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 B8 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........00 00 00 00 00 00 00 00-00 00 0 00 00 00 00 00  *...........

can anyone see where i am going wrong? and maybe come up with a way to fix it? sorry for the long post

**quzah** · 08-01-2006

Code:

while( fgets( buf, BUFSIZ, fp ) != NULL )
{
    if( (ptr = strstr( buf, ": " )) )
    {
        strncpy( output, ptr + 2, 48 );
        output[ 24 ] = ' ';
        output[ 48 ] = '\0';
        puts( output );
    }
}

Close enough for who it's for.

Quzah.

**sbeehre** · 08-01-2006

Thanks for your reply! i really appreciate it

what should i define ptr as and what is output? is that the outtxtfile fp?

also i changed the first line to

Code:

while( fgets( instring, 200, textfile ) != NULL )

is that right?

**Salem** · 08-01-2006

> is that right?
Yes.
The "why you shouldn't use feof() in a loop" is in the FAQ.
Quzah's answer fixes that problem.

Also, you might want to use
sizeof(instring) rather than 200, so the code automatically tracks the declaration of your array.

**quzah** · 08-01-2006

ptr is a pointer to a char, because that's what the function strstr returns.
output would simply be another buffer, since you can't strncpy to a file...

puts takes a pointer to a char as its argument, so that also could have clued you in as to what output is.

Quzah.

**sbeehre** · 08-02-2006

Originally Posted by quzah

ptr is a pointer to a char, because that's what the function strstr returns.
output would simply be another buffer, since you can't strncpy to a file...

puts takes a pointer to a char as its argument, so that also could have clued you in as to what output is.

Quzah.

ok i have changed my program around with your suggestions and it almost works

this is the new one

Code:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <string.h>

int main()
{

  char instring[200];
  char output[200];
  int charpos;  // position of ":" in the string
  FILE *textfile,*outtxtfile ;

  charpos=10;
  // Process file
  textfile=fopen("dump.txt","r");
  // open the destination file
  outtxtfile=fopen("outtext.txt","w");

 // process file
while( fgets( instring, sizeof(instring), textfile ) != NULL )
{
    if( (charpos = strstr( instring, ": " )) )
    {
        strncpy( output, charpos + 1, 48 );
        output[ 24 ] = ' ';
        output[ 48 ] = '\0';
        puts( output );
    }
}
  fclose(textfile);
  fclose(outtxtfile);

  return 0;
}

it outputs to the screen perfectly as shown below

Code:

 4D 5A 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 B8 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

How do i get it to write like that to a file? do i change puts( output ) to fputs ( output , outtxtfile) ?

**sbeehre** · 08-02-2006

ok i tried fputs (output , outtxtfile) and it doesnt format correctly in the outout text file, its like its not putting end of line breaks in or something as the file is just one big long line.

**sbeehre** · 08-02-2006

also one thing i didnt mention is that the file is actually over 1000 lines long.... the first piece of text was just the first few lines, will that make any difference in the running of the program? i didnt think it would so i didnt mention it before.

**whiteflags** · 08-02-2006

> its like its not putting end of line breaks in or something as the file is just one big long line.
Put a newline character in the string then.

> also one thing i didnt mention is that the file is actually over 1000 lines long.... will that make any difference in the running of the program
No, nothing noticable.

**sbeehre** · 08-02-2006

the \n in the string worked a treat... but when i use the dump.txt with 1179 lines in it i get nothing in the outtext.txt file, but with the small dump.txt it works perfectly.

**whiteflags** · 08-02-2006

Did you open the right files for reading and writing?

Did you check if fopen returned a valid file pointer?

Is there something about the big version of dump.txt that you're not telling us?

**sbeehre** · 08-02-2006

i know the im opening the right files because if i use the dump file in my first post it works perfectly. The big file is just more of the same as the small dump file and has 2 blank lines at the bottom.

**sbeehre** · 08-02-2006

anyone?

**quzah** · 08-02-2006

Post your code.

Quzah.

**Tonto** · 08-02-2006

i know the im opening the right files because if i use the dump file in my first post it works perfectly. The big file is just more of the same as the small dump file and has 2 blank lines at the bottom.

That's not a very good 'know'. You should check fopen to see if it returns a NULL file handle.

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