How to use libapt (or libept) in debian-like system to list packages and get their infos?

Question

Somebody used libapt or libept to list packages and get informations about package in a debian-like system?

Libapt is not well-documented at all, and i've found few examples and tutorials about libept. Can someone explain me best methods to

1. get a list of every packages in the apt-system
2. get informations about single packages (like name, version, dependences, description, etc.
3. get list of files installed by a single package

Work directly with apt internal files is quite simple, but i want to use a library to respect apt specifications.

Answer 1

In debian there is a package called libapt-pkg-doc which contains some documentation (like an API reference). Once installed, you can access it at file:///usr/share/doc/libapt-pkg-doc/html/index.xhtml.

I only just had a look at libapt and here is what I have learned so far:

How to list all packages:

#include <apt-pkg/cachefile.h>
#include <apt-pkg/pkgcache.h>

int main() {
    // _config and _system are defined in the libapt header files
    pkgInitConfig(*_config);
    pkgInitSystem(*_config, _system);

    pkgCacheFile cache_file;
    pkgCache* cache = cache_file.GetPkgCache();

    for (pkgCache::PkgIterator package = cache->PkgBegin(); !package.end(); package++) {
        std::cout << package.Name() << std::endl;
    }

    return 0;
}

Answer 2

Take a look at how apt-cache(8) is implemented. Obtaining the source with apt is easy:

# apt-get source apt

In the source file cmdline/apt-cache.cc theres is a function called DumpPackage() which extracts information from a named file in the cache.