Solved

zlib inflate c example

Posted on 2010-08-30
13
991 Views
Last Modified: 2012-05-10
Hi,

Given an array that contains zlib compressed data, can you give me the code to decompress the data and store it in another array?
0
Comment
Question by:PMembrey
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 6
  • 5
  • 2
13 Comments
 
LVL 33

Expert Comment

by:pgnatyuk
ID: 33564671
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 33564676
The official web page of zlib contains a nice overview of how to use the deflate and inflate functionality :

        http://www.zlib.net/zlib_how.html
0
 

Author Comment

by:PMembrey
ID: 33564677
That one is where I started - but it's written on the assumption that the data is being read directly from a file. I tried going through lib.h and looking at the documentation there, but it didn't take much for me to get very stuck :-)
0
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

Author Comment

by:PMembrey
ID: 33564702
That's the example I was working through but it makes calls to fread() whereas I just have an array.
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 33564703
Reading from a file is not very different than reading from a buffer in memory.

Just leave out the fread calls, and instead, simply point to your memory buffer that holds the compressed data.

Similarly, you can leave out the fwrite calls, and use a memory buffer for output.
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 33564706
>> simply point to your memory buffer that holds the compressed data.

You'll note that in the example code, the two buffers used are called 'in' and 'out'. Just replace those with yours, and you're all set.
0
 

Author Comment

by:PMembrey
ID: 33564713
So given two arrays, one containing the compressed version and one empty for the decompressed version - what would an example code fragment be?

0
 
LVL 33

Assisted Solution

by:pgnatyuk
pgnatyuk earned 200 total points
ID: 33564791
This is my working code:
uLongf destLen = buffSize;
int err = uncompress( (Bytef *)pBuff, &destLen, (const Bytef *)pData, pSize);
pBuff is a memory block (void*) - the destination
pData - the source.
 
0
 

Author Comment

by:PMembrey
ID: 33564910
pgnatyuk, you've got the points as I've got the example to work - but could you add to your example how to find out how much data was decompressed?  i.e. if I want to write that out to a file, I need to know the length of the decompressed data :-)
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 33564911
>> what would an example code fragment be?

Something like :
unsigned char in_buffer[IN_SIZE];             /* compressed data : IN_SIZE bytes */
unsigned char out_buffer[OUT_SIZE];           /* make sure OUT_SIZE is big enough to hold the decompressed data */

z_stream strm;

strm.zalloc = Z_NULL;
strm.zfree = Z_NULL;
strm.opaque = Z_NULL;

strm.avail_in = 0;
strm.next_in = Z_NULL;

ret = inflateInit(&strm);
if (ret != Z_OK) {
    /* oops : handle this as an error, and stop */
}

strm.avail_in = IN_SIZE;
strm.next_in = in_buffer;
strm.avail_out = OUT_SIZE;
strm.next_out = out_buffer;

ret = inflate(&strm, Z_NO_FLUSH);
if (ret != Z_STREAM_END) {
    /* oops : the data wasn't completely processed - handle this */
}

inflateEnd(&strm);

Open in new window

0
 
LVL 53

Accepted Solution

by:
Infinity08 earned 300 total points
ID: 33564928
>> I need to know the length of the decompressed data :-)

strm.total_out will hold that value.
0
 

Author Comment

by:PMembrey
ID: 33564936
hmm, looks like I will split the points :-)

But I'd still like to know how to update the first example so that it provides the decompressed data size....
0
 
LVL 53

Expert Comment

by:Infinity08
ID: 33564977
>> But I'd still like to know how to update the first example so that it provides the decompressed data size....

When using uncompress, destLen will hold the size of the decompressed data.
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Have you thought about creating an iPhone application (app), but didn't even know where to get started? Here's how: ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Important pre-programming comments: I’ve never tri…
An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
The goal of this video is to provide viewers with basic examples to understand recursion in the C programming language.
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use for-loops in the C programming language.

710 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question