Binary files and conversion

[timmu]

I'd like to read binary files and generate an output consisting of normal 8-bit numerical values corresponding to the bytes.
In other words, the input is a binary fine and output should be an array of values 0-255.

1. How should the file be opened/read?
2. Is there an automatic conversion from binary to 8-bit?

Thank you!

[Lesiok]

What do you think is the difference between binary data and bytes with values ​​from 0-255 ?

[timmu]

Hi Lesiok,

There is no difference, the data are always stored as binary. In the text format there are things like newline character etc. My question was:
What would be the best way to get this conversion done and should that involve opening and reading the files in another way (such as using different file handling commands and classes) specific to Qt.

Thanks.

[Lesiok]

What conversion ? You say : there is no difference. Can tell precisely what is binary file. Are this data formatted or this is a stream of bytes.
P.S.
You are asking about QDataStream or QFile

[timmu]

Hi,

What I mean is how to read it byte by byte and do the conversion so that the output is a text file with numbers between 0 and 255.

Thanks

[Lesiok]

RTFM - read this funny manual
To read data from file use QFile and to write this data to text file use QTextStream. And next time simple ask : how write data to text file.

[anda_skoa]

What I mean is how to read it byte by byte and do the conversion so that the output is a text file with numbers between 0 and 255.

Just read from the input device using the QIODevice read API and use QString::number() on each byte, or read fixed sized blocks and create strings for each block by using QString::sprintf with as many arguments as you have bytes in your blocks.

Cheers,
_

[timmu]

I was wondering why the code below doesn't work. I'm trying to read a binary file byte by bite and convert it into text or numbers, preferably to numbers.

char readChar;
 
QFile infile(Inname); if(!infile.open(QIODevice::ReadOnly)) {exit(1);}
QTextStream in_stream(&infile);
 
QFile outfile(Outname); if(!outfile.open(QIODevice::WriteOnly | QIODevice::Text)) {exit(1);}
QTextStream out_stream(&outfile);
 
 
while(!in_stream.atEnd())
{
  in_stream >> readChar;
  if(in_stream.atEnd()) {break;}
  out_stream << readChar << "\n";
}

char readChar;

QFile infile(Inname); if(!infile.open(QIODevice::ReadOnly)) {exit(1);}
QTextStream in_stream(&infile);

QFile outfile(Outname); if(!outfile.open(QIODevice::WriteOnly | QIODevice::Text)) {exit(1);}
QTextStream out_stream(&outfile);


while(!in_stream.atEnd())
{
  in_stream >> readChar;
  if(in_stream.atEnd()) {break;}
  out_stream << readChar << "\n";
}

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Then this should also allow reading binary file but how to convert it into int?:

qint64 bufSize = 1024;
char *buf = new char[bufSize];
qint64 dataSize;
while (!in_stream.atEnd()) 
{
  dataSize = infile.read(buf, bufSize);
}

qint64 bufSize = 1024;
char *buf = new char[bufSize];
qint64 dataSize;
while (!in_stream.atEnd()) 
{
  dataSize = infile.read(buf, bufSize);
}

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[Lesiok]

Because You are using variable of type char. So if in readChar You have value 65 decimal in text file You will get letter A because 65 is ASCII code of letter A. In first example change line 14 to :

out_stream << (int)readChar << "\n";

out_stream << (int)readChar << "\n";

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This is abc of C/C++ language and have nothing to Qt.

[timmu]

Thank you very much, this made it work. Now I have this problem:

The following script only outputs the values whose 'signed 8-bit value' is positive. If it is negative, the corresponding value is not written into the output file. Why is that?

char readChar;
 
QFile infile(Inname); if(!infile.open(QIODevice::ReadOnly)) {exit(1);}
QTextStream in_stream(&infile);
 
QFile outfile(Outname); if(!outfile.open(QIODevice::WriteOnly | QIODevice::Text)) {exit(1);}
QTextStream out_stream(&outfile);
 
 
while(!in_stream.atEnd())
{
  in_stream >> readChar;
  if(in_stream.atEnd()) {break;}
  out_stream << (int)readChar << "\n";
}

char readChar;
 
QFile infile(Inname); if(!infile.open(QIODevice::ReadOnly)) {exit(1);}
QTextStream in_stream(&infile);
 
QFile outfile(Outname); if(!outfile.open(QIODevice::WriteOnly | QIODevice::Text)) {exit(1);}
QTextStream out_stream(&outfile);
 
 
while(!in_stream.atEnd())
{
  in_stream >> readChar;
  if(in_stream.atEnd()) {break;}
  out_stream << (int)readChar << "\n";
}

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[anda_skoa]

Try

out_stream << QString::number(static_cast<uchar>(readChar))

out_stream << QString::number(static_cast<uchar>(readChar))

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Cheers,
_

[wysota]

If your file contains binary data then why are you reading it with QTextStream?

[timmu]

Hi Wysota,

How would you recommend to read the file? The code change recommended above didn't solve the problem, I'm still not seeing all of the binary values converted to numbers.

Thanks!

[wysota]

How would you recommend to read the file?

With QFile and its QIODevice API.

What I understand is that you simply want a hex dump of the file. The most trivial approach (albeit far from optimal in terms of memory) is:

QFile in("infile");
QFile out("outfile");
in.open(QIODevice::ReadOnly);
out.open(QIODevice::WriteOnly);
out.write(in.readAll().toHex());

QFile in("infile");
QFile out("outfile");
in.open(QIODevice::ReadOnly);
out.open(QIODevice::WriteOnly);
out.write(in.readAll().toHex());

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You can do the same if you want a decimal encoding, only that you need to iterate over each byte in the array and convert it manually to a decimal value.

[timmu]

Thanks Wysota, this is a very good idea. Indeed, I actually need decimal encoding. If I need to iterate over each byte to make the conversion, then I cannot use readAll(), is that correct? In that case I need to look at each byte individually somehow.

[wysota]

If I need to iterate over each byte to make the conversion, then I cannot use readAll(), is that correct?

You can use readAll(). You can't use toHex().

[timmu]

I've been playing with the code below. I'd like to read all the bytes of the binary file "infile" one by one and output all the bits (in the form of 1/0) so that I get one number per line per line. Example:
1
0
1
1
0
1
0
0

What is the best way to achieve that?

QFile in("infile");
QFile out("outfile");
in.open(QIODevice::ReadOnly);
out.open(QIODevice::WriteOnly);
out.write(in.readAll());

QFile in("infile");
QFile out("outfile");
in.open(QIODevice::ReadOnly);
out.open(QIODevice::WriteOnly);
out.write(in.readAll());

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[wysota]

What is the best way to achieve that?

The same as earlier. Read data and convert it to the notation of your choice. One byte is eight bits. For each byte extract each subsequent bit and print it.

[timmu]

Thanks.

I guess my question was how to do it byte by byte.

[wysota]

I guess my question was how to do it byte by byte.

while(!file.atEnd()) {
  char c;
  if(!file.readChar(&c)) break;
  print_bit_by_bit(c);
}

while(!file.atEnd()) {
  char c;
  if(!file.readChar(&c)) break;
  print_bit_by_bit(c);
}

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