I have a text file that I want to compress after it gets an specified size. I've already seen GZipStream which works great, but RAR compression is much better.
I've been looking for a library that can compress a file with RAR (I really don't care about extracting or uncompressing), but I couldn't find one yet.
As the RAR compression algorithm isn't free (only the decompression algorithm is), you won't find a library for it (or have to purchase a license).
A good alternative is the LZMA SDK that delivers the compression algorithms used in 7-Zip.
For a compression ratio/speed comparison, you can have a look e.g. at the Maximum Compression summary page, ranks 50 and 52, comparing WinRAR 4.01 in "Best Solid" mode and 7-Zip 9.22 in "Ultra" mode. WinRAR compresses only slightly better (<1%) and faster, 7-Zip decompresses faster.
Note that, as peachykeen noted, if you look at the efficiency ratings instead of size, WinRAR in normal mode is much faster than 7-Zip.
来源：https://stackoverflow.com/questions/8084783/compress-a-file-with-rar