reading bytes out of a file

Hello there

I am trying to parse a file by reading the bytes from it (ideally hex).

But I have a snag...

any bytes over the value of 127 give me problems (i.e. -128 etc).

How can i read the bytes out of the array.

for example. i have 2 qbytearrays here:

Code:

---

count = 6;
arrayParse = array.mid(b,2);

---

(the data contained within these two bytes is b00d)

if i try to read the first byte, i get a negative number.

how can i read it so i get the correct value?

or if that fails, how can i just read the file as hex??

(sorry if this is a chumps question!)

and in case you need more info, i have opened the file using file.open(QIODevice::ReadOnly);

Please try to give a self contained example. Your 2 lines are not understandable - lacking context etc.

A char is (usually) signed and has (integer) values from -128 to +127. Use unsigned char if you want 0 to 255.

And apropos QByteArrays: how did you write those to that file?

If you know what type of data is in the file then read it as the correct type rather than as an array of chars, which is what I assume you are doing.

Do something like this:

Code:

---

QFile file(fileName);
if (!file.open(QIODevice::ReadOnly)) {
    // out put some debug
    return;
}
 
QDataStream in(&file);
in.setByteOrder(QDataStream::LittleEndian);    // or what ever order determined from where originating machine type (or how written)
in.skipRawData(2);    // skip some data
qint16 val1;
in >> val1;
// continue reading appropriate types from the input

---

usually will have a check for end of file e.g.: while(!in.atEnd())

Hope this is clear enough

thanks for you input.

i will try to give some more information.

I am trying to analyse the data contained within a hex file.

so for example:

Code:

---

array = file.readAll(); 
int numBytes = array.length();
 
if (numBytes > 0 )
    {
        a = 0;      // counter for position in the array
 
while (( a < numBytes ) && (data_parsed == 0))
        {
            long sequenceCode = 0;
 
            a = array.indexOf(71, a);      // looking for hex 47
            std::cout << "position of first 47 hex byte =  " << a << std::endl;
 
            arrayReadBytes = array.mid(a,3);
            b = a+3;
 
...

---

so basically i need to search the required file for certain bytes and then act on them.

Then later on, I am checking the following bytes:

Code:

---

QByteArray array2;
array2 = array.mid(b,2);

---

its at this point that I fall down, as i mentioned before, i am overflowing.

As for using QDatastream, I have checked the documentation, and I can't seem to see the search functionality that i had from using a qbytearray....

ok, and (disregarding such things as endianness etc...) doesn't

Code:

---

QDataStream ds(array2);
qint16 i;
ds >> i;

---

work for you?

(If you are on the same machine that wrote the file, maybe something like

Code:

---

qint16 i = *reinterpret_cast<const qint16*>(array.constData()+b)

---

will work, too.)

I managed to get some information out, using your idea

qint16 i = *reinterpret_cast<const qint16*>(array.constData()+b)

but changed it to qint8 to read 1 byte instead (i don't always want to use 2 bytes)

hopefully i can get on with it now!

while i am still here..

is there an easy way to keep the leading zeros in the number???

i.e.

value in the file = 0d

after reading out the value = d

leading zeros... that is not a question of reading data, but of output formatting.
How do you print the value so far? Are you aware of QString::arg()? There are overloads that allow you to specify fieldwidth, base and fill-character.

HTH