How to format my output using ofstream

Hi, I have a quick question on formatting.

I am writing a program that takes a buffer of type char* and writes it to a logfile via

logfile << (unsigned int*)bufffer1[i];


Unfortunately, the output is always in the format

0x000000E00x0000001F0x0000001E0x00000081

I would like to put it into the format

E0 1F 1E 81

but I can't figure out how to do it with ofstream. The code is below and kind of quick and dirty. I have thousands of these strings to look at, so if anyone has any idea I'd greatly appreciate it. Thanks for your time.

~Steve

// Compares a nonfunctional mpeg and the same file made functional
#include <fstream.h>
#include <iomanip>

const char * file1 = "test.mpeg";
const char * file2 = "testcorrected.mpeg";


int main ()
{
unsigned char *buffer1;
unsigned char *buffer2;
unsigned char *buffer3;
long size1;
long size2;
long tot_byteoffsets = 0;
ifstream file1 (file1, ios::in | ios::binary | ios::ate);
ifstream file2 (file2, ios::in|ios::binary|ios::ate);
size1 = file1.tellg();
size2 = file2.tellg();
file1.seekg (0, ios::beg);
file2.seekg(0, ios::beg);
buffer1 = new unsigned char [size1];
buffer2 = new unsigned char [size2];
buffer3 = new unsigned char [size1];
file1.read(buffer1, size1);
file2.read(buffer2, size2);
file1.close();
file2.close();

// Setup log file
ofstream logfile("logfile.txt");

logfile << "Starting log \n\n" ;


cout << "the complete file is in a buffer" << endl;
cout << "The file size is " << size1 << endl;
cout << "Starting compare" << endl;

//Main comparison loop
int i = 0;
int j = 0;

while (i < size1)
{
if(buffer1[i] == buffer2[j])
{
buffer3[j] = buffer1[i];
i++;
j++;
}
else
{
int bytechange = 0;
logfile << "The following string differs at byte offset " << i << endl;
while((buffer1[i] != buffer2[j]) || (buffer1[i+1] != buffer2[j+1]) ||
(buffer1[i+2]!= buffer2[j+2]))
{
bytechange++;

logfile << (unsigned int*) buffer1[i];
if (bytechange%4 == 0)
logfile << " ";
i++;
}

logfile << "\nTotal bytes - " << bytechange<< endl << endl;

//j++;
tot_byteoffsets += bytechange;
buffer3[j] = buffer1[i];
}


}

//write mpegfile based on comparison
ofstream myFile ("output.mpeg", ios::out | ios::binary);
myFile.write(buffer3,(size1-tot_byteoffsets));

cout << "Total kilobytes difference is " << (tot_byteoffsets/1024) << endl;



delete[] buffer1;
delete[] buffer2;
delete[] buffer3;
return 0;
}

if you write in binary file the output will be written in binary form as is the case here.

Regards

Hi,

The ofstream is not flagged as anything, and the data has to be read into binary for the ifstream but if I do

logfile.hex

the output is the same. Thanks for the hand, do you know how to fix this.

~Steve

Hi,

The pointer is not required for the unsigned int cast.

logfile<<setbase(16)<<(unsigned int)buffer1[i]<<" ";

Here is some of the output from the log file.

Starting log

The following string differs at byte offset 36
bd 29 40 8 40 4c 1b d9 b e0 2b c4 5a 8e 0 bc 84 82 4a 18 4a 51 50.................

You really need to add checks in your code and make sure it won't result in access violations, particularly in the while loops. I have a feeling that this is a school assignment...am I correct?

TDM

This problem had me freak out for quite some time. The problem imho, that the standard c++ library does not make any difference in the implementation of:

Code:

---

ostream& operator<<( const char );
ostream& operator<<( const unsigned char);

---

while I believe it should take the first as a character and the second as a short short int.

Here is how I finally solved it. Consider the string s to contain binary data (yes, c++ strings can contain binary data without problems). The "& 0xff" thing might be a bit hacky, but it was what got the whole thing working.

Code:

---

void hexdump( ostream& o, const string& s )
{
  // save the current state of o
  const ios::fmtflags old_flags = o.flags();
  o << hex;
  for ( unsigned long i = 0; i < s.length(); ++i )
    o << setw(2) << setfill('0') << (s[i] & 0xff) << ' ';
  // restore the old state of o
  o.setf( old_flags );
}

---

Hi TDM,
Its not a school assignment, I'm just not very good with byte streams. I bought a Creative DVCR TV card, and I shouldn't have skimped ...

It writes a non-standard MPEG stream, that when multiplexed can't be read by windows MPEG demultiplexers. However I found and old MS demultiplexer that I was able to modify to work. Unfortunately, it is very difficult to read the code for the parser, so I am taking the test mpeg stream, running it through the demultiplexer and dumping the output to file. I believe the rules to be easy (and preliminary analysis suggests they are), so this is my way of seeing them. Once I figure out the rules, I'll be able to finish my Directshow filter and be able to write a compliant mpeg2 stream from my (now worthless) card. Thanks for all of your help.

~Steve

P.S. There aren't any violations, although for a more general program, I agree it would be a good idea.

Looking at the other posts, I am now wondering why I am having such problems with putting out a hexdump of a std::string. Can anybody explain me why the following code

Code:

---

  const unsigned char data[] = { 0, 127, 128, 255 };
  for ( unsigned int i = 0; i < 4; ++i )
    cout << setbase(16) << (unsigned int)data[i] << ' ';
  cout << endl;

  const string s( (char*)data, 4 );
  for ( unsigned int i = 0; i < 4; ++i )
    cout << setbase(16) << (unsigned int)s[i] << ' ';
  cout << endl;

---

gives the following output

0 7f 80 ff
0 7f ffffff80 ffffffff

Thanks for enlightenment.