I would like to use gzip from C++ (or C) to gzip a string. If possible, I would like to use zlib.

When I learned that I would have to use zlib to compress and uncompress, I Googled it for a few minutes and then quickly wrote a program to gzip a file and then ungzip it. However, I don't actually have any need to do that. I need to use gzip to compress and uncompress a string, not a file. I couldn't find much good documentation for using gzip on strings. Every example I find works with files.

Could someone show me a simple example?

Thanks in advance.

Brandon

I should add that when I say a "string," I mean a char[], although if I see an example that applies to C++ strings, one can easily convert back and forth.

Well you could take your program and remove the file IO parts

You can use zlib's utility functions compress() and uncompress().

Thanks. I was thinking that I might have to figure out deflate() and inflate(). Could you give an example? Can it be made to produce a gzip header?

probably this helps: http://stackoverflow.com/questions/4...ffer-with-zlib

Thanks, Pan. I guess my question would be whether it's possible to create it with gzip headers instead of zlib headers.

gzip doesn't have headers, the program interface of gzip is zlib

Zlib and gzip both produce headers in the encoded object and they aren't the same.

Oh, sorry, you meant file headers...

Or if the encoding is in memory, of the encoded structure in memory. I Googled this thing for several hours yesterday.

For a test I have compared the output of zlib.minigzip and gzip; the first three bytes of the file-headers are the same (1f 8b 08), but gzip also stores the original file name/attributes:

So does minigzip do compression on a memory variable and, if so, what functions does it call to do it?

no it uses gzopen/gzwrite/etc

BTW: have you read this: http://www.zlib.net/zlib_faq.html#faq20

Since gzopen()/gzwrite() work with files, I am not surprised that minigzip creates the same file headers as gzip. The issue is getting zlib calls to do it.

After posting the first message here yesterday, I did come across that link and read the relevant portion. According to that, I would have to use deflate/deflateInit2. If that is what I have to do, I must say that the proper settings of the parameters to deflateInit2() to produce a gzip type header are not well documented. Something about adding 16 to windowsBits. I would really like to see an explicit example of compressing and uncompressing using zlib programmed to duplicate gzip.

Why, it is in gzio.c in zlib source, check deflateInit2 in function gz_open, and writing crc in gzclose.

PS: Or, if you want to handle files in memory, fmemopen(3) might be useful.