[SOLVED] Overwrite specific bytes without reading the whole file, QFile

faenil

Hi guys :)

I have been looking for a way to overwrite specific files in a file, but could only find something about memory mapping the file...let me explain :)

let's suppose I want to overwrite byte 0x51B...I use this code

@ QFile cre("C:/stubs/200159ED.cre");
if (!cre.open(QIODevice::WriteOnly)) return -10;
cre.seek(0x51B);
QDataStream crestream(&cre;);
qint8 attempt = 1;
crestream << attempt;
cre.close()@

the problem is the file is first erased, and then it's filled with 0s, until 0x51B is reached, which is correctly set to 01...

Is there any way I can avoid erasing the whole file before writing into it?

I'd also like to avoid reading the whole file, changing some bits, and then writing it back to a new file, because the file could be pretty big :)

Thanks in advance :)

faenil

dangelog

Yep. WriteOnly will silently truncate. Open the file with ReadWrite.

cf. https://qt.gitorious.org/qt/qt/blobs/master/src/corelib/io/qfsfileengine.cpp#line201

faenil

thank you very much :) and thanks for the precious link :)

sfilippidis

If your initial question is answered and you consider the issue solved, please edit your initial post to change the title from

Overwrite specific bytes without reading the whole file, QFile

to

[SOLVED] Overwrite specific bytes without reading the whole file, QFile

faenil

I'll try it tomorrow morning and check if it's solved ;) thanks for the tip anyway ;)

sfilippidis

[quote author="faenil" date="1312059979"]I'll try it tomorrow morning and check if it's solved ;) thanks for the tip anyway ;) [/quote]

Even better! :-)