How to read a binary file in C : binary, c, file, read

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06.16.2004 at 02:38AM PDT, ID: 21027080

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5.8

How to read a binary file in C

Zone: C Programming Language

Tags: binary, c, file, read

As I am working in Java since 5 years, I started forgetting the concepts of C :(.

I am not able to read the binary files such as Word Documents and PDFs into my buffer .

I used fopen and fread
I used open and read.

in both the options I have failed.

Please post me one working example

Thanks
Sudhakar

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Question Stats

Zone: Programming

Question Asked By: sudhakar_koundinya

Solution Provided By: sunnycoder

Participating Experts: 5

Solution Grade: A

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06.16.2004 at 02:39AM PDT, ID: 11322723

sudhakar_koundinya:

Here is the example

FILE *stream;
char buffer[513];
int i, ch;

/* Open file to read line from: */
if( (stream = fopen( "c:\\a.doc", "rb" )) == NULL )
exit( 0 );

/* Read in first 80 characters and place them in "buffer": */
ch = fgetc( stream );
for( i=0; (i < 513 ) ; i++ )
{
buffer[i] = (char)ch;
ch = fgetc( stream );
printf("\n%d %d",i,ch);
}

/* Add null to end string */
buffer[i] = '\0';
printf( "%s\n", buffer );
fclose( stream );

I have tried, but not working for binary files

06.16.2004 at 02:40AM PDT, ID: 11322733

Sys_Prog:

Hi sudhakar_koundinya,

This link has a working example

http://www.cplusplus.com/ref/cstdio/fread.html

Cheers!

Assisted Solution

06.16.2004 at 02:43AM PDT, ID: 11322746

Rank: Sage

sunnycoder:

Hi sudhakar_koundinya,
> ch = fgetc( stream );
> for( i=0; (i < 513 ) ; i++ )
> {
> buffer[i] = (char)ch;
> ch = fgetc( stream );
> printf("\n%d %d",i,ch);
> }

use fread instead of fgetc or fgets

FILE *in = fopen("in_file.txt","r");
FILE *out = fopen("out_file.txt","w");

in len;
char buffer[1024];

while((len = fread(buffer,1,sizeof(buffer),in)) > 0)
{
fwrite(buffer,1,len,out);
}

fclose(in);
fclose(out);

of course you need better error handling

check these links

http://www.experts-exchange.com/Programming/Programming_Languages/C/Q_20587923.html
http://www.experts-exchange.com/Programming/Programming_Languages/C/Q_10081782.html

Sunnycoder

Accepted Solution

06.16.2004 at 02:58AM PDT, ID: 11322790

Rank: Sage

sunnycoder:

Hi Sudhakar,

FILE *stream;
char buffer[513];
int i, ch;

/* Open file to read line from: */
if( (stream = fopen( "c:\\a.doc", "rb" )) == NULL )
exit( 0 );

/* Read in first 80 characters and place them in "buffer": */ <<<<< 512 bytes
ch = fgetc( stream );
for( i=0; (i < 513 ) ; i++ )
{
buffer[i] = (char)ch;
ch = fgetc( stream );
printf("\n%d %d",i,ch); <<<<<< you will get equivalent int printed here ... good enough ... Note that first character read will not be printed.
}

/* Add null to end string */
buffer[i] = '\0'; <<<<<<<<<<<, not a good idea ... 0 and other such characters and character sequences can occur anywhere within binary data ... Depending on a terminator character for binary data is definitely bad idea ... You will be better off with the sound knowledge of the number of chracters you have read

printf( "%s\n", buffer ); >>>>> Since the file is binary, most likely you will get gibbersih which will terminate as soon as 0 occurs in the buffer ... That is the way strings (%s) behaves .... remember that this is not a string but binary data ... If you wish tp print it, use fwrite instead ... Something like
fwrite ( buffer, 1, 513, stdout);
stdout, is defined in stdio.h

fclose( stream );

cheers
sunnycoder

06.16.2004 at 03:01AM PDT, ID: 11322810

sudhakar_koundinya:

Hello All,

Thanks for the immediate responses, but the problem is still continuing

//Reading methods
int IOUtils::readFully(FILE* in,unsigned char b[],int length )
{
      return readFully(in,b,0,length);
      return 0;
}

int IOUtils::readFully(FILE* in, unsigned char b[] , int off, int len)
{

            //int got=fread(b,sizeof(unsigned char), 1,in);
             int got=fread(b, 1,sizeof(b),in);
             return got;


}

//implemetation methods

HeaderBlockReader::HeaderBlockReader(char* file)
{
      FILE* fp=fopen(file,"rb");
      //int fp=_open(file,O_RDONLY);
      if(fp>0)
      {
            unsigned char* _data=new unsigned char[512];
            _data = new unsigned char[512];
       IOUtils *utils=new IOUtils();
int i = utils->readFully(fp, _data,512);
            printf("%d",i);
            if(i!=512)
            {
                  printf(" nota microsoft document");
            }
            else
            {
                  LongField *longfield = new LongField(0, _data);

                  printf(" Possible it could be a Microsoft Document %x",longfield->get());
            }
      }
      else
      {
                        printf(" Document does not exists");
      }
      fcloseall();
}

06.16.2004 at 03:03AM PDT, ID: 11322815

Rank: Sage

sunnycoder:

this is C++ ... I would suggest sticking to either C or C++ ... you are mixing the C++ code with C programming style

06.16.2004 at 03:07AM PDT, ID: 11322832

sudhakar_koundinya:

Yes I do agrre,

When I worked on this previously, i never faced the problems.

Now this is immediate requirement for me. to integrate c,c++ and java files and strucking in file reading concepts :(

06.16.2004 at 03:09AM PDT, ID: 11322849

Rank: Sage

sunnycoder:

check http:#11322790 for reason why your code was not working and http:#11322746 for a working example

06.16.2004 at 03:16AM PDT, ID: 11322871

sudhakar_koundinya:

>> int got=fread(b, 1,sizeof(b),in);

but i am doing the same know? Then what is the reason for not working

06.16.2004 at 03:31AM PDT, ID: 11322926

Rank: Sage

sunnycoder:

>Then what is the reason for not working

What is the output you see ?

06.16.2004 at 03:42AM PDT, ID: 11322969

sudhakar_koundinya:

instead of reading all 512 bytes it is just reading 6 bytes

06.16.2004 at 03:46AM PDT, ID: 11322988

sudhakar_koundinya:

As you said, intgrating c and c++ may gives problems

I just done a test run on document of size 19kb. but the out put i got is of 20 kb

here is the test program

#include <io.h>
#include <stdio.h>

void main()
{
       FILE *in = fopen("c:\\a.doc","rb");
      FILE *out = fopen("c:\\out_file.doc","w");

      int len;
      char buffer[1024];

      while((len = fread(buffer,1,sizeof(buffer),in)) > 0)
      {
       fwrite(buffer,1,len,out);
      }

      fclose(in);
      fclose(out);
}

06.16.2004 at 03:46AM PDT, ID: 11322990

Rank: Sage

sunnycoder:

Nope, it is just printing 6 bytes ... see my comment http:#11322790

/* Add null to end string */
buffer[i] = '\0'; <<<<<<<<<<<, not a good idea ... 0 and other such characters and character sequences can occur anywhere within binary data ... Depending on a terminator character for binary data is definitely bad idea ... You will be better off with the sound knowledge of the number of chracters you have read

printf( "%s\n", buffer ); >>>>> Since the file is binary, most likely you will get gibbersih which will terminate as soon as 0 occurs in the buffer ... That is the way strings (%s) behaves .... remember that this is not a string but binary data ... If you wish tp print it, use fwrite instead ... Something like
fwrite ( buffer, 1, 513, stdout);
stdout, is defined in stdio.h

06.16.2004 at 03:47AM PDT, ID: 11322995

Rank: Sage

sunnycoder:

>I just done a test run on document of size 19kb. but the out put i got is of 20 kb
try comparing the files ... Are you sure you are not seeing size on disk for doc2 ... Also, which platform and which compiler ?

06.16.2004 at 03:52AM PDT, ID: 11323024

sudhakar_koundinya:

>>buffer[i] = '\0'; <<<<<<<<<<<, not a good idea ...

after removing that code only i am getting this error

I am compiling the program on v