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Solved
Replace value in QByteArray & QDataStream
Posted on 2011-03-10
Hi experts,
I'm trying without success to replace some values in a byte array or in a data stream in QT 4.7
Here's my situation:
I have a binary file with data. Each two bytes of this file represent a signed integer value. I need to replace all the integer values which are 0 with 22 and save the file with the new values.
Any ideas how to proceed ?
Thanks,
Peter
I'm trying without success to replace some values in a byte array or in a data stream in QT 4.7
Here's my situation:
I have a binary file with data. Each two bytes of this file represent a signed integer value. I need to replace all the integer values which are 0 with 22 and save the file with the new values.
Any ideas how to proceed ?
Thanks,
Peter
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6 Comments
Unless there is an issue with byte order, you should be able to open the file in read/write mode, and call the Read function passing the pointer to a DWORD variable and reading two bytes. If the variable has a value of 0, seek backwards 2 bytes and write the value 22.
CFile f;
f.Open( strFileName, CFile::modeRead | CFile::modeWrite );
DWORD i;
const DWORD v22 = 22;
while( f.Read( &i, 2 ) == 2 )
{
if( i == 0 )
{
f.Seek( -2, CFile::current );
f.Write( &v22 );
}
}
If there is an issue with byte order, then you just need to replace v22=22 with v22=0x1600;
CFile f;
f.Open( strFileName, CFile::modeRead | CFile::modeWrite );
DWORD i;
const DWORD v22 = 22;
while( f.Read( &i, 2 ) == 2 )
{
if( i == 0 )
{
f.Seek( -2, CFile::current );
f.Write( &v22 );
}
}
If there is an issue with byte order, then you just need to replace v22=22 with v22=0x1600;
Opps... that should have been something like
f.Write( &v22, 2 )
and you might have to type case the pointers to get something like this to properly compile.
f.Write( &v22, 2 )
and you might have to type case the pointers to get something like this to properly compile.
Sorry, I haven't explained very clear what I want to do here...
The file which is saved is not the same file (the source file). I need to move all the data from the source file to a QByteArray and in the process change the 0 values to 22. Then, I need to compress this byte array with qCompress and only then write it to a newly created file.
So, my problem is that I have to move the data from the source file to the byte array and change to zeros...
All the best,
Peter
The file which is saved is not the same file (the source file). I need to move all the data from the source file to a QByteArray and in the process change the 0 values to 22. Then, I need to compress this byte array with qCompress and only then write it to a newly created file.
So, my problem is that I have to move the data from the source file to the byte array and change to zeros...
All the best,
Peter
Active 1 day ago
you could read the file using std::ifstream in binary mode:
std::ifstream infile("xxx.dat", std::ios_base::in | std::ios_base::binary);
qint16 q16;
while (infile.read((char*)(&q16)
{
}
note the qint16 should be 2 bytes what i have taken for granted.
the in loop you could check on 0 and replace by 22. then add to QByteArray
QByteArray qarr;
...
if (q16 == 0)
q16 = 22;
qarr.append((char*)(&q16),
note, the QByteArray would get binary data that way, same as in the file. if you need hexstring conversion you mast do a conversion first.
Sara
std::ifstream infile("xxx.dat", std::ios_base::in | std::ios_base::binary);
qint16 q16;
while (infile.read((char*)(&q16)
{
}
note the qint16 should be 2 bytes what i have taken for granted.
the in loop you could check on 0 and replace by 22. then add to QByteArray
QByteArray qarr;
...
if (q16 == 0)
q16 = 22;
qarr.append((char*)(&q16),
note, the QByteArray would get binary data that way, same as in the file. if you need hexstring conversion you mast do a conversion first.
Sara
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