I have got a file which is let's say 8 bytes length. For example it looks like that:
22222222
Now, I read first let's say 5 bytes and changing them. For ex. to 11111
Finally, I want to write them ONTO EXCISTING DATA to the file, so I expect the file to look like that:
11111222
But I get only 11111, because file is erased. How can I disable erasing? (Maybe this question exists, but couldn`t find question like this one)
Depending on what you are exactly doing with the file, you might want to memory map it:
QFile f("The file");
f.open(QIODevice::ReadWrite);
uchar *buffer = f.map(0, 5);
// The following line will edit (both read from and write to)
// the file without clearing it first:
for (int i=0; i<5; ++i) buffer[i] -= 1;
f.unmap(buffer);
f.close();