problem reading files in C

I'm using the fgetc() function for reading files.Aside from reading files I want it to read files such as EXEs as well.I test it by using a hex editor to insert 0200 0242 and then run the program.The problem is when I put it after a hex string like 0000 0000 0000 0000 the program will not read it instead it will terminate.Otherwise it will read it and report the match

Code:

int dvd_chk(FILE *x)
{
int num_chk=0;
char c;
while( (c = fgetc( x )) != EOF )
{
if ( c == 0x02 ) { c=fgetc(x);
if ( c == 0x00 ) { c=fgetc(x);
if ( c == 0x04 ) { c=fgetc(x);
if ( c == 0x24 ) { num_chk++; }
}}}
}
fclose( x );
return match;

hmmm....I'm not so sure if you can do that, read in a char and test it with a hex value. probably can...I'm not too sure about it, though.

Also, you need to open the file - try adding....

x = fopen("somefile.txt","rb"); //you need to open it as rb which is reading in binary mode

to your first line of code in that function.

I open the file through main and pass the file pointer to the function.I've tested it by using Hex Workshop and adding the hex string 0200 0424.I tried it on a text file and an EXE.Here is the full code:

Code:

#include <stdio.h>

int dvd_chk(FILE *x);

int main(int argc, char *argv[])
{
FILE *inf;
int noc;
printf("DVD Check finder\n\n");
if (argc!=2){
printf("insufficient program usage\n");
printf("usage: dvdchk <file to be scanned>\n");
return 0;
}
inf=fopen( argv[1], "rb" );
if (inf==null){
printf("File %s does not exist\n");
return 0;
}
noc=dvd_chk(inf);
printf("Number of Checks: %d\n",noc);
return 0;
}

int dvd_chk(FILE *x)
{
int match=0;
char c;
while( (c = fgetc( x )) != EOF )
{
if ( c == 0x02 ) { c=fgetc(x);
if ( c == 0x00 ) { c=fgetc(x);
if ( c == 0x04 ) { c=fgetc(x);
if ( c == 0x24 ) { match++; }
}}}
}
fclose( x );
return match;
}

HHHHHHMMMM

don't you need to use fread() to read binary files?

Originally posted by SPOOK
HHHHHHMMMM

don't you need to use fread() to read binary files?

I think fgetc should work fine if the file is opened in the binary mode.

from http://www.acm.uiuc.edu/webmonkeys/book/c_guide
*************************************************
Declaration:

int fgetc(FILE *stream);
Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream.
On success the character is returned. If the end-of-file is encountered, then EOF is returned and the end-of-file indicator is set. If an error occurs then the error indicator for the stream is set and EOF is returned.
*************************************************

Doesnt put any restrictions on the stream . As far I know , in most unix C compilers there is no difference between the modes , in windoze/dos I think the \r\n combination is converted to a single \n while reading and \n is output as \r\n while writing in the text mode , I may be wrong .

Your problem (I believe) is with the way you're checking EOF. EOF is not in the range of a char. You should use an integer for 'c'. All 'is*()' functions, '*getc()' functions, *putc() functions, take and receive a "char" as an "int". EOF is _NOT_ in the range of a char.

Code:

int dvd_chk(FILE *x)
{
   int match=0;
   int c;

   if( x == NULL ) return -1;

   while( (c = fgetc( x ) ) != EOF )
   {
      if ( c == 0x02 ) { c=fgetc(x);
         if ( c == 0x00 ) { c=fgetc(x);
            if ( c == 0x04 ) { c=fgetc(x);
               if ( c == 0x24 ) { match++; }
      }}}
   }
   fclose( x );
   return match;
}

Why are you closing the file in this function? You don't open it here, why close it here?

Quzah.

Originally posted by SPOOK
HHHHHHMMMM

don't you need to use fread() to read binary files?

yes

I think you can use feof() to judge the end of the file , You can have a test.
It's my suggestion.

Originally posted by swoopy


yes

Why do you think only fread and fwrite can be used with binary files and not fgetc ? I havent seen any such thing in any reference .
This code copied all whatever exes in windoze I tried perfectly.

#include <stdio.h>
int main(void)
{
int c;
FILE *fin,*fout;
char bufin[256],bufout[256];
printf("Give the name of the input file:");
gets(bufin);
printf("Give the name of the output file:");
gets(bufout);
fin=fopen(bufin,"rb");
if(fin==NULL)
{
printf("Unable to open %s\n",bufin);
perror(NULL);
return 1;
}
fout=fopen(bufout,"wb+");
if(fout==NULL)
{
printf("Unable to create %s\n",bufout);
perror(NULL);
return 1;
}
while( (c=fgetc(fin)) != EOF) fputc(c,fout);
return 0;
}

pinko_liberal,

yes, you are right. My mistake.