I'm opening a file and getting a QTextStream of it. I am then reading the stream line by line using readLine(). When the line matches a certain string, I need to replace it with another string. I need the behaviour to be that the line is completely replaced (ie, if the line was "longword" and I replace it with "word", the line should contain "word" and "word" only).
At the moment I am using seek() and then the << operator to put my string in at the given location, but the remnants of the last string remain, so I am left with something like "wordword". How can I prevent this from happening and ensure the entire previous line is fully replaced with my new one?
To my knowledge, you cannot simply remove a chunk of a text file in-place. If the replacement string was identical in size, you might be able to replace those exact bytes, and if it were shorter you might be able to hack around the problem by filling the empty space with nulls.
If you didn't want to do that, you would have to create a new file, read each line from the old file, make any required changes to that line in memory, then write that line out to the new file. Once this is complete, you could then replace the original file with the new file.
If it were possible to add/remove chunks to/from the file, you would most likely be left with a considerably fragmented file on the HDD. If you needed to insert more characters, extra fragments would have to be created as the new data simply couldn't fit in the amount of space occupied by the old data, and removing data would leave holes in the file.