How do I get package versions in c++? (linux)

Question

I've been writing a program that needs a wine version of 2.6 or later. I'd like to get it as a boolean, so I've been trying to use the code below:

#include <string>
#include <iostream>
#include "WineCheck.h"
#include <cstdlib>

using namespace std;

bool checkForWine()
{
    // Create variables for checking wine state
    bool wineIsThere   = false;
    bool wineIsVersion = false;

    // Check dpkg if wine is there
    if (string(system("dpkg -l | cut -c 4-9 | grep \\ wine\\ ")) == " wine ")
        {
        wineIsThere = true;
        // Check version
        if (double(system("wine --version | cut -c 6-8")) >= 2.6)
            wineIsVersion = true;
        }

    // Return
    if (wineIsThere && wineIsVersion)
        return true;
    else
        return false;
}

Answer 1

First, it's my opinion you shouldn't bother with this. Wine 2.6 should just be included as a dependency in your configuration script, and/or your package file. Targeting a specific package management system in your program source code is not a good idea if you want to maintain portability to other GNU/Linux distributions that don't use that packager.

To answer your question though. There are two ways I found you can do this. You can check /var/lib/dpkg/status. Read through the file line by line until you get to this section. If you don't find the section, or the Status: ... line doesn't say installed then wine is not installed. The Version: ... line will tell you what version is installed. I verified this method works by installing and uninstalling Wine on Debian Wheezy. You didn't say what distro you're working with, but it's obvious you're using the Debian Packaging system, so this should work on Ubuntu and other Debian based distributions as well.

$cat /var/lib/dpkg/status
...
Package: wine
Status: install ok installed
Priority: optional
Section: otherosf
Installed-Size: 80
Maintainer: Debian Wine Party <pkg-wine-party@lists.alioth.debian.org>
Architecture: amd64
Version: 1.4.1-4
...

The other option is use libdpkg. I found an example that lists all installed packages.

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

#include <sys/types.h>
#include <sys/stat.h>

#include <dpkg/dpkg.h>
#include <dpkg/dpkg-db.h>
#include <dpkg/pkg-array.h>
#include "filesdb.h"

const char thisname[] = "example1";

int
main(int argc, const char *const *argv)
{
    struct pkg_array array;
    struct pkginfo *pkg;
    int i;
    enum modstatdb_rw msdb_status;

    standard_startup();
    filesdbinit();
    msdb_status = modstatdb_open(msdbrw_readonly);
    pkg_infodb_init(msdb_status);

    pkg_array_init_from_db(&array);
    pkg_array_sort(&array, pkg_sorter_by_name);

    for (i = 0; i < array.n_pkgs; i++) {
        pkg = array.pkgs[i];
        if (pkg->status == stat_notinstalled)
            continue;
        printf("Package --> %s\n", pkg->set->name);
    }

    pkg_array_destroy(&array);

    modstatdb_shutdown();
    standard_shutdown();

}