zlib Problems

[nathanpc]

Hello,
I'm learning C++, and i'm developing a simple zipper application, as my own, here is my code:

#include <string>
#include <stdexcept>
#include <iostream>
#include <iomanip>
#include <sstream>
#include "zlib.h"
using namespace std;

string compress_string(const string& str,
                            int compressionlevel = Z_BEST_COMPRESSION)
{
    z_stream zs;                        // z_stream is zlib's control structure
    memset(&zs, 0, sizeof(zs));

    if (deflateInit(&zs, compressionlevel) != Z_OK)
        throw(runtime_error("deflateInit failed while compressing."));

    zs.next_in = (Bytef*)str.data();
    zs.avail_in = str.size();           // set the z_stream's input

    int ret;
    char outbuffer[32768];
    string outstring;

    // retrieve the compressed bytes blockwise
    do {
        zs.next_out = reinterpret_cast<Bytef*>(outbuffer);
        zs.avail_out = sizeof(outbuffer);

        ret = deflate(&zs, Z_FINISH);

        if (outstring.size() < zs.total_out) {
            // append the block to the output string
            outstring.append(outbuffer,
                             zs.total_out - outstring.size());
        }
    } while (ret == Z_OK);

    deflateEnd(&zs);

    if (ret != Z_STREAM_END) {          // an error occurred that was not EOF
        ostringstream oss;
        oss << "Exception during zlib compression: (" << ret << ") " << zs.msg;
        throw(runtime_error(oss.str()));
    }

    return outstring;
}

int main(int argc, char* argv[])
{
    string allinput;

    while (cin.good())     // read all input from cin
    {
        char inbuffer[32768];
        cin.read(inbuffer, sizeof(inbuffer));
        allinput.append(inbuffer, cin.gcount());
    }
        string cstr = compress_string( allinput );

        cerr << "Deflated data: "
                  << allinput.size() << " -> " << cstr.size()
                  << " (" << setprecision(1) << fixed
                  << ( (1.0 - (float)cstr.size() / (float)allinput.size()) * 100.0)
                  << "% saved).\n";

        cout << cstr;
 return 0;
}

Then i executed it normally, without errors, but when i try to open the archive i have some errors:
*.gz

gzip: /home/ubuntu/test.txt.gz: not in gzip format

*.zip

[/home/ubuntu/test.zip]
  End-of-central-directory signature not found.  Either this file is not
  a zipfile, or it constitutes one disk of a multi-part archive.  In the
  latter case the central directory and zipfile comment will be found on
  the last disk(s) of this archive.
zipinfo:  cannot find zipfile directory in one of /home/ubuntu/test.zip or
          /home/ubuntu/test.zip.zip, and cannot find /home/ubuntu/test.zip.ZIP, period.

If you want to see the full discussion about this application, See Here

Thanks,
Nathan Paulino Campos

[rags_to_riches]

Actually, that doesn't look like it's your code at all, it looks like it's this guy's code.

[tabstop]

I also don't see where you write anything to a file. If you redirected output, you'll have to get rid of the informational stuff at the top.

[nathanpc]

The code is from that guy, but then how i can do this code function!

Thanks!

[tabstop]

So did you look at the zlib manual? Even a little bit?

[nathanpc]

I took a look on the Usage Example, but that code is so much confusing, the thing that i want is the most simple code, only to compress a test file and study that code to start the improvement of it.
If you can help me i'll be very happy

Thanks!

[tabstop]

The sample code you linked to is 36 lines to compress a file, with pages of comments to keep it from being confusing. If you're that kind of person and take out all the error checking, you're left with deflateInit, deflate+fwrite, deflateEnd.

[nathanpc]

I didn't understand!

[nathanpc]

Please, someone can help me!
The only thing that i want is to start, then i will continue by myself!

Thanks!

[vart]

if you think this code is confusing - write a code that just calls external pkzip.exe with correct parameters, it will be much simplier

[nathanpc]

Hello vart,
First thing, i use Linux. Second thing, i want to build my own zipper, your suggestion was good, but i want to build my own project.

Thanks,
Nathan Paulino Campos

[VirtualAce]

Zlib is very simple to use and the docs are pretty clear about how to use it. Perhaps a bit more reading and less asking before reading is in order.

[leeor_net]

I think what you're missing is the point that if you can't understand basic code that is generally well documented than you need to work with C++ more. ZLib is a very simple library and has a well documented API not to mention dozens and dozens of examples. Clearly you're not understanding them which means that you're more likely having difficulty understand C++ itself, not ZLib.