calamares-settings-ubuntu/common/modules/pkgselectprocess/checkpackage-backend.cpp

#include <iostream>
#include <string>
#include <apt-pkg/algorithms.h>
#include <apt-pkg/cacheiterators.h>
#include <apt-pkg/init.h>
#include <apt-pkg/cachefile.h>
#include <apt-pkg/pkgcache.h>
#include <apt-pkg/pkgsystem.h>
#include <apt-pkg/progress.h>

int main(int argc, char* argv[]) {
    pkgInitConfig(*_config);
    pkgInitSystem(*_config, _system);
    if (_system == 0) {
        std::cerr << "apt-pkg not initialized\n";
        return 1;
    }

    // Open the package cache.
    pkgCacheFile *cache = new pkgCacheFile();
    OpProgress progress;
    if (!cache || cache->Open(&progress, false) == false) {
        std::cerr << "Error: could not open APT cache.\n";
        return 1;
    }
    pkgApplyStatus(*cache);

    std::vector<std::string> package_names(argv + 1, argv + argc);
    if (package_names.empty()) return 0;

    for (std::string package_name : package_names) {
        pkgCache::PkgIterator it = cache->GetPkgCache()->FindPkg(package_name);
        if (!it.end()) std::cout << package_name << " ";
    }

    std::cout << "\n";
    cache->Close();
    return 0;
}