Copying two files in a third one...
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Yes that was what I had in mind last night but it was kind of late so I went with the "simpler" solution. BTW I already warned him about merging files that contain format headers, this is applicable ONLY for raw data.
For specific formats the concatenation must also be format specific, you must know how to parse that file, read in header tags and process them and only merge the raw data.
I was also thinking about pre-allocating the output file to the size of both inputs so that fragmentation can be avoided.
Since we are now talking BIG files, it would be wise to abort the operation early on in case there is not enough free space on disk, not merge the files all the way to 90% and fail just then, when time has been waster and the entire disk has been filled, which may have other negative implications.
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Well, specific file formats typically have a header, which defines properties, such as bitrate, color depth, resolution, after which follows the raw data.
For example, if you want to join two images together, you have to read the resolution and color depth, figure out how you want to compose the two input images into the output image, do some conversion if the data is in a different format and so on.
Take a look here for example, this is a wikipedia article on BMP image format and its header:
http://en.wikipedia.org/wiki/BMP_file_format#Bitmap_file_header -
Never assume that the user of your application will only ever use it for what you anticipate!
If your application can concatenate two files some user will end up trying to concatenate two blueray films with it;-)
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Aha, okay I get it now thanks. What about .zip files, that's what I am mostly interested about...
Can I zip a file through my application? For example, there is a button for file creation, then another one checking if the file really exists and then a button called add to archive, where I put the file in question, in a .7z, .rar archive.
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[quote author="Tobias Hunger" date="1329983973"]Never assume that the user of your application will only ever use it for what you anticipate!
If your application can concatenate two files some user will end up trying to concatenate two blueray films with it;-)[/quote]
Hehe, nice one indeed! The thing is that the user will not be able to select the files for concatenation. It would be predetermined in the application code, so that is not a big issue.
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Well, it is not like something REALLY bad will happen, worst case scenario the procedure will fail in numerous possible ways. Luckily no one's foot will be literally shot off :)
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[quote author="croussou" date="1329984083"]Aha, okay I get it now thanks. What about .zip files, that's what I am mostly interested about...
Can I zip a file through my application? For example, there is a button for file creation, then another one checking if the file really exists and then a button called add to archive, where I put the file in question, in a .7z, .rar archive.[/quote]
No, it will not work with archives such as zip or 7z. Archives have headers as well. Those headers describe which files or folders are in the archive, and where their data can be found inside the file.
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According to "wikipedia":http://en.wikipedia.org/wiki/Zip_(file_format)#File_headers, the .zip file format DOES feature a header that contains plenty of information:
bq. 0 4 Local file header signature = 0x04034b50 (read as a little-endian number)
4 2 Version needed to extract (minimum)
6 2 General purpose bit flag
8 2 Compression method
10 2 File last modification time
12 2 File last modification date
14 4 CRC-32
18 4 Compressed size
22 4 Uncompressed size
26 2 File name length (n)
28 2 Extra field length (m)
30 n File nameIt is pretty much safe to assume if you use this method to join two zip files you will get what MIGHT appear as a good file, but IT WILL BE CORRUPTED.
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You have no option but use the archive format API to merge two archives together.
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[quote author="ddriver" date="1329984668"]You have no option but use the archive format API to merge two archives together.[/quote]
I don't want to merge :) I just want to save a file that I read from my application in a .zip format. For example a text file, I want to be able to add it in an archive on the desktop through the app that is.
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[quote author="croussou" date="1329984584"]It was mostly a general question, if there is any way for an application to provide files in an archive :)
Not about concatenation itself...just the zipping process.[/quote]
Grmbl!
Then please, why do you only say that now? Why do you send us down a different road, trying to answer the question you asked instead of the question you have? Please spend a bit more time formulating your actual question in the future; describe what you want to achieve, not how you think you might achieve it. That will make us spend our time more efficiently.Anyway, working with ZIP files is a "FAQ":http://developer.qt.nokia.com/faq/answer/how_to_compress_data_with_qt on this site. There is "plenty":http://developer.qt.nokia.com/search?search=zip to be found on this site on this topic.
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Again, you have to use the format API. Or reimplement everything yourself which is not really applicable.
Luckily most archive formats have an open API so they can easily be integrated.
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Relax, we are all flawed by design - that is what life is for, polishing those flaws ;)
Take a look here:
http://www.7-zip.org/sdk.htmlbq. LZMA SDK includes:
C++ source code for .7z compression and decompression (reduced version)This is no longer Qt territory, but you can easily integrate the 7zip library and use it in your Qt project.
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You cannot expect others to write all your code for you, you have to learn it for yourself, and it does take time. Even if your get all the code snippets from others, without the proper skills you will not be able to put them together in a working program. Rome wasn't built overnight you know ;)