issue char * hex buffer to QString conversion to print to textEdit Widget

[bobth12]

Hi,

I am new to QT, but have been programming in C/C++. I have a question regarding displaying hex values to TextEdit Widget. I have tried various method, but sometimes some of the hex values change or sometime the output is totally different.

So I have a char buffer like this:

1st implementation:


char * cHexData = new char [HexBuff_size+1];
memset(cHexData, '\0', HexBuff_size+1);
char * temp_iter = cHexData;

for (int i = 0; i<(HexBuff_size+1); i++){
sprintf(temp_iter ,"%X",(unsigned char)HexBuff[i]); //HexBuff is char buffer of size 256 and it holds the some data
temp_iter++; // I am printing putting the values to cHexData buffer which will hold hex values
} //ex: cHexData = FF6C69.....


//now i need to convert it to QString so that I can out the same Hex value in cHexData with formatting
for (int i = 0; i<(HexBuff_size+1); i++){

if (i!=0 && i%2==0) //append whitespace every 2 char
QTtext_qsPrintData+=" ";

if(i!=0 && i%16 ==0) //every 16th hex value newline
QTtext_qsPrintData+= "\n";

QTtext_qsPrintData+=QString(QChar(cHexData[i]));
}

ui->textWid->setText(QTtext_qsPrintData);

//output i want is;
//FF 6C 69... <- so same hex value as in cHexData.
//25 C8 95...
//...



So this implementation; when in Debug mode(breakpoints) has the correct Hex value for QTtext_qsPrintData as cHexData, which is good. But in the release version, on every run, some of the Hex values in QTtext_qsPrintData changes. That in turn will display the values wrong on the output
So after reading about hex value and QString conversion; I tried the following:




...
iNumWhiteSpace = (HexBuff_size/2); //number of whitespace between 2 hex values
iNumReturns = (HexBuff_size/16)-1; //\n every 16th hex value;

for(int i = 0 ; i<HexBuff_size; i ++){
if (i!=0 && i%2==0){
*temp_iter=' ';
temp_iter++;
}
if(i!=0 && i%16 ==0){
*temp_iter='\n';
temp_iter++;
}

sprintf(temp_iter ,"%X",(unsigned char)HexBuff[i]);
temp_iter++;

}

q_bHex = QByteArray(reinterpret_cast<char*>(cHexData ), HexBuff_size+iNumWhiteSpace+iNumReturns+1);
//and QByteArray q_bHex(cHexData , HexBuff_size+iNumWhiteSpace+iNumReturns+1);
ui->textWid->setText(QString(q_bHex));



// This implementation is also same as above

I have also looked into something like; but the values are decimal, and that make sense since my char * buffer already have hex values.


//for (int i=0 ; i < HexBuff_size; i++)
// QTtext_qsPrintData+= QString("%1").arg(cHexData[i],0,16);



please help with this. I was not too sure if I should post it here or QT newbie; If I have posted it in the wrong forum please move it.

Thanks!

[Infinity]

Just convert each character of your C-style character array to an integer and add it to a QString:


QString result;
result.reserve(3 * arraySize - 1);
for(char* i = array, end = array + arraySize; i < end; ++i) {
if(!result.isEmpty()) {
result += QLatin1Char(' ');
}
result += QString("%1").arg(static_cast<uint>(*i), 2, 16, QLatin1Char('0'));
}
hexLineEdit->setText(result);

That's just an quick draft. I haven't tested it.
I recommend to avoid the usage of C-style arrays and C-style casts in C++.

[ChrisW67]

This code is faulty and dangerous.


char * cHexData = new char [HexBuff_size+1];
memset(cHexData, '\0', HexBuff_size+1);
char * temp_iter = cHexData;

for (int i = 0; i<(HexBuff_size+1); i++){
sprintf(temp_iter ,"%X",(unsigned char)HexBuff[i]); //HexBuff is char buffer of size 256 and it holds the some data
temp_iter++; // I am printing putting the values to cHexData buffer which will hold hex values
} //ex: cHexData = FF6C69.....



If you are going to convert N bytes into a hexadecimal string you need a target buffer at least 2N+1 bytes long to avoid the possibility of overrunning the buffer. In this case, your 256 source bytes require a 513 byte output buffer.

You convert each successive byte into one (i.e. no 0 padding for values < 16) or two hexadecimal digits in the target buffer and then advance the pointer by one character. You need to consistently convert each byte to two characters ("%02X") and advance by two chars.

If you already have the input buffer and know its size:


QByteArray temp = QByteArray::fromRawData(input, inputBufferSize);
QString output = QString(temp.toHex());

[bobth12]

Hi ChrisW67,

You are absolutely correct. That was not the original size. My code did do [2*size+1+other sizes] which needed me to show my other codes. So just for simplicity i did that; for sprintf I used "%.2X".


--Back to the topic.

This is weird. Not sure what happened...now before ChrisW67's modification i tired I Infinity's



QString result;
result.reserve(3 * arraySize - 1); // <------------at this line I was getting Malloc(): memory corruption:confused:
for(char* i = array, end = array + arraySize; i < end; ++i) {
if(!result.isEmpty()) {


So i removed your code Infinity's suggestion and tried ChrisW67

Still I get this Malloc(): memory corruption.

When i commented ChrisW67's suggestion out and make it look like before where the code worked. The memory corruption issue is still show. So i tried re-starting the machine, tired re-creating the project; no luck.

Here is my code after the QString conversion function.


tempData = QByteArray::fromRawData(cHexData , ((HexBuff_size*2)+iSizeofWhite+iSizeofRet+1) );
QTtext_qsPrintData= QString(tempData.toHex());

ui->textWid->setText(QTtext_qsPrintData);
delete [] cHexData ;
cHexData = NULL;
temp_iter= NULL;



If I comment out lines 1-4 I get the following:
double free or corruption (!prev):...
malloc(): memory corruption:...

But it worked before. :confused:

Thanks!

Added after 1 44 minutes:

Okay so i was able to fix the memory corruption issue. However, I am still having trouble with outputting hex values



tempData = QByteArray::fromRawData(cHexData , ((HexBuff_size*2)+iSizeofWhite+iSizeofRet+1) );
QTtext_qsPrintData= QString(tempData.toHex());

ui->textWid->setText(QTtext_qsPrintData);


After line 4 the values displayed in the GUI are all decimal values. If i put a breakpoint, tempData has the correct hex values. But doing tempData.toHex() converts everything to decimal. Please note: cHexData already has hex values. I want to display those values.

[Infinity]

I've tested my code. There have been mistakes, but none of them leads to memory corruption.
Just for completeness, that's a slightly improved version of my former draft which seems to work:


static const int width = 5;
QString result;
result.reserve(3 * arraySize - 1);
int numInLine = 0;
for(unsigned char *i = array, *end = array + arraySize; i < end; ++i, ++numInLine) {
if(numInLine >= width) {
result += QLatin1Char('\n');
numInLine = 0;
}
if(numInLine > 0) {
result += QLatin1Char(' ');
}
result += QString("%1").arg(static_cast<int>(*i), 2, 16, QLatin1Char('0'));
}

Using the toHex method of QByteArray class has the disadvantage that you don't get whitespaces and new lines, but it should work of course. I think the way you're filling your array is the problem. Show us the relevant code.

cHexData already has hex values
Your variable contains a number. The binary system is used to store the value internally (and to do calculations). The decimal or hexadecimal number system comes only into play when displaying the number.

[ChrisW67]

Please note: cHexData already has hex values. I want to display those values.
If cHexData is a pointer to a C-style string of [0-9A-F] and whitespace chars that you simply want to display then:


const char *cHexData = "51 74 20 43 65 6E 74 72 65";
QString result(cHexData);
// or
QString result = QString::fromLatin1(cHexData);

or if the buffer is not NUL terminated:


const char cHexData[] = {'5', '1', ' ', '7', '4', ' ', '2', '0', ' ', '4', '3', ' ', '6', '5', ' ', '6', 'E', ' ', '7', '4', ' ', '7', '2', ' ', '6', '5'};
const int charCount = sizeof(cHexData);

QString result = QString::fromLatin1(cHexData, charCount);

[bobth12]

Hi,

Thanks to both of you for the support.

I went with:


QString result = QString::fromLatin1(cHexData, charCount);