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Re: Read a binary file

#11

Sep 5th, 2007

why not just do it the quick and easy way, assuming the binary file is no larger than the char buffer. If the size is unknown than we'd have to first find out the file size and allocate the buffer appropriately. In any case it will be a lot faster then reading the fine one byte at a time.

Also, make sure to open the file in binary mode, not the default text mode.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
unsigned char iobuf[1024];
 
fileread.read(iobuf,sizeof(iobuf));
unsigned char iobuf[1024];

fileread.read(iobuf,sizeof(iobuf));

Aother problem with using std::string like that is that std::string can not be typecast into a structure like character buffers can. The contents of the binary file may well be a structure and reading it into a std::string would destroy that.

Last edited by Ancient Dragon; Sep 5th, 2007 at 1:32 pm.

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Re: Read a binary file

#12

Sep 5th, 2007

>> .. really mad. It,s not displays as a binary code, I mean bunch of zeros and ones.

if all you want to do is display the contents of a file as a sequence of bits (i presume that is what you mean by bunch of zeros and ones),

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <fstream>
#include <limits>
#include <bitset>
#include <iostream>
using namespace std;
 
int main()
{
  ifstream file( __FILE__ ) ; file >> noskipws ;
  typedef bitset< numeric_limits<unsigned char>::digits > bitset ;
  unsigned char byte ;
  while( file >> byte ) cout << bitset(byte) ;
}
#include <fstream>
#include <limits>
#include <bitset>
#include <iostream>
using namespace std;

int main()
{
  ifstream file( __FILE__ ) ; file >> noskipws ;
  typedef bitset< numeric_limits<unsigned char>::digits > bitset ;
  unsigned char byte ;
  while( file >> byte ) cout << bitset(byte) ;
}

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Re: Read a binary file

#13

Sep 5th, 2007

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why not just do it the quick and easy way

Because the quick and easy way is usually more costly in the long run?

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In any case it will be a lot faster then reading the fine one byte at a time.

You don't have to read it one byte at a time if that's what you're worried about.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
// Get the binary data
char iobuf[1024];
 
while ( fileread.read( iobuf, sizeof( iobuf ) ) {
  contents += iobuf;
}
// Get the binary data
char iobuf[1024];

while ( fileread.read( iobuf, sizeof( iobuf ) ) {
  contents += iobuf;
}

Now you don't have to worry about buffer sizes, or find the size of the file, or worry about allocating and freeing memory.

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Aother problem with using std::string like that is that std::string can not be typecast into a structure like character buffers can. The contents of the binary file may well be a structure and reading it into a std::string would destroy that.

Why can't you do it? A string has the data() method, and I don't understand why (somestruct)iobuf is any different from (somestruct)contents.data() if they both have the same characters.

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Re: Read a binary file

#14

Sep 5th, 2007

Do you need to read in your file as binary, or is it just a plain text file?

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Re: Read a binary file

#15

Sep 5th, 2007

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Originally Posted by Hamrick

Because the quick and easy way is usually more costly in the long run?

How's that? can you show an example?

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Originally Posted by Hamrick

You don't have to read it one byte at a time if that's what you're worried about.
Help with Code Tags

C++ Syntax (Toggle Plain Text)
// Get the binary data
char iobuf[1024];
 
while ( fileread.read( iobuf, sizeof( iobuf ) ) {
  contents += iobuf;
}
// Get the binary data char iobuf[1024]; while ( fileread.read( iobuf, sizeof( iobuf ) ) { contents += iobuf; }

I don't think std::string class will work with binary data like that. I think the += operator will stop when it encounters the first 0 byte in the iobuf.

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Originally Posted by Hamrick

Why can't you do it? A string has the data() method, and I don't understand why (somestruct)iobuf is any different from (somestruct)contents.data() if they both have the same characters.

I don't see a difference either (1) if it works (see above comment) and (2) except that old farts like me just perfer using char arrays when the problem suits it better

Last edited by Ancient Dragon; Sep 5th, 2007 at 3:18 pm.

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Re: Read a binary file

#16

Sep 5th, 2007

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How's that? can you show an example?

I can't, but my teachers like to say that if you don't do something right the first time, you end up doing it again and again to fix the problems. It seems to me that using an array is bad because you lock yourself into a buffer size, and using allocated memory is bad because you have to work harder to make it work right and keep it working. The C++ string fixes both of those because it grows on its own and you don't have to manage it.

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I don't think std::string class will work with binary data like that. I think the += operator will stop when it encounters the first 0 byte in the iobuf.

Yeah, I tried it. But assign and append let you pick a count for the incoming string. This works.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
 
using namespace std;
 
#define SETUP 1
 
int main() {
  string contents;
 
#ifdef SETUP
  ofstream binaryOut( "binary.dat", ios::binary );
 
  contents.assign( "C code.\0C code run.\0Run code run.", 33 );
  binaryOut.write( contents.data(), contents.size() );
 
  binaryOut.close();
#else
  ifstream binaryIn( "binary.dat", ios::binary );
 
  // Get the binary data
  char iobuf[1024];
 
  do {
    binaryIn.read( iobuf, sizeof( iobuf ) );
    contents.append( iobuf, binaryIn.gcount() );
  } while ( binaryIn );
 
  binaryIn.close();
 
  // Print the characters
  for ( int i = 0; i < contents.size(); ++i ) {
    if ( !isprint( contents[i] ) ) {
      cout<< int( contents[i] );
    } else {
      cout<< contents[i];
    }
  }
 
  cout<<"\n";
#endif
 
  return 0;
}
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>

using namespace std;

#define SETUP 1

int main() {
  string contents;

#ifdef SETUP
  ofstream binaryOut( "binary.dat", ios::binary );

  contents.assign( "C code.\0C code run.\0Run code run.", 33 );
  binaryOut.write( contents.data(), contents.size() );

  binaryOut.close();
#else
  ifstream binaryIn( "binary.dat", ios::binary );

  // Get the binary data
  char iobuf[1024];

  do {
    binaryIn.read( iobuf, sizeof( iobuf ) );
    contents.append( iobuf, binaryIn.gcount() );
  } while ( binaryIn );

  binaryIn.close();

  // Print the characters
  for ( int i = 0; i < contents.size(); ++i ) {
    if ( !isprint( contents[i] ) ) {
      cout<< int( contents[i] );
    } else {
      cout<< contents[i];
    }
  }

  cout<<"\n";
#endif

  return 0;
}

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and (2) except that old farts like me just perfer using char arrays when the problem suits it better

But does the problem really suit char arrays better or are the old farts just doing what they're comfortable with?

If the file is always a fixed size that's great, but if it's not you have to make a super huge char array to accommodate the expected sizes and add extra logic in case the size is bigger than the array. If you don't want to wrestle with that, you have to dynamically allocate a char array, and that's just a lot of memory management that you don't need to do. It makes the code longer and harder to keep up.

Last edited by Hamrick; Sep 5th, 2007 at 3:57 pm.

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Re: Read a binary file

#17

Sep 5th, 2007

>>I can't, but my teachers like to say that if you don't do something right the first time, you end up doing it again and again to fix the problems
And your teachers are right. Sofware companies spend probably three times (or more) the money in program maintenance then in original development.

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Re: Read a binary file

#18

Sep 5th, 2007

One thing that the OP could clarify is whether or not it is necessary to read the whole file into memory, or whether it might simply be simpler and easier to process as a stream.

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Re: Read a binary file

#19

Sep 6th, 2007

•

Originally Posted by Hamrick

How does that make a difference? A string just handles the memory for the char array instead of making you do it. I don't think there should be any problem with using a string as long as you don't do any text conversions.
Help with Code Tags

C++ Syntax (Toggle Plain Text)
ifstream fileread ("path to the binary file");
string contents;
char ch;
 
// Get the binary data
while ( fileread.get( ch ) ) {
  contents.push_back( ch );
}
 
// Print the binary data as hex
for ( int i = 0; i < contents.size(); ++i ) {
  cout<< hex << int( contents[i] ) <<" ";
}
 
fileread.close();
ifstream fileread ("path to the binary file"); string contents; char ch; // Get the binary data while ( fileread.get( ch ) ) { contents.push_back( ch ); } // Print the binary data as hex for ( int i = 0; i < contents.size(); ++i ) { cout<< hex << int( contents[i] ) <<" "; } fileread.close();

Actually later I want to convert some parts to decimal.

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Re: Read a binary file

#20

Sep 6th, 2007

•

Originally Posted by vijayan121

>> .. really mad. It,s not displays as a binary code, I mean bunch of zeros and ones.

if all you want to do is display the contents of a file as a sequence of bits (i presume that is what you mean by bunch of zeros and ones),
Help with Code Tags

C++ Syntax (Toggle Plain Text)
#include <fstream>
#include <limits>
#include <bitset>
#include <iostream>
using namespace std;
 
int main()
{
  ifstream file( __FILE__ ) ; file >> noskipws ;
  typedef bitset< numeric_limits<unsigned char>::digits > bitset ;
  unsigned char byte ;
  while( file >> byte ) cout << bitset(byte) ;
}
#include <fstream> #include <limits> #include <bitset> #include <iostream> using namespace std; int main() { ifstream file( __FILE__ ) ; file >> noskipws ; typedef bitset< numeric_limits<unsigned char>::digits > bitset ; unsigned char byte ; while( file >> byte ) cout << bitset(byte) ; }