Find differences in two xml files doesn't return anything

I have a problem with my code. It looks for two xml files, a.xml and b.xml. When I don't have those files and run it I get the message "Can't find input files".

When I do have both the files, my program doesn't return anything at all, when I would expect it to say "Found files" at least, but was hoping it would print out the difference nodes in the two files.

#include "pugi/pugixml.hpp"

#include <iostream>
#include <string>
#include <map>

int main() {
    pugi::xml_document doca, docb;
    std::map<std::string, pugi::xml_node> mapa, mapb;

    if (!doca.load_file("a.xml") || !docb.load_file("b.xml"))
        std::cout << "Can't find input files";
        return 1;

    std::cout << "Found files";    

    for (auto& node: doca.child("site_entries").children("entry")) {
        const char* id = node.child_value("id");
        mapa[id] = node;
    }

    for (auto& node: docb.child("site_entries").children("entry")) {
        const char* idcs = node.child_value("id");
        if (!mapa.erase(idcs)) {
            mapb[idcs] = node;
        }
    }

    for (auto& ea: mapa) {
        std::cout << "Removed:" << std::endl;
        ea.second.print(std::cout);
    }

    for (auto& eb: mapb) {
        std::cout << "Added:" << std::endl;
        eb.second.print(std::cout);
    }

}

Can anyone tell me where I have gone wrong?

a.xml

<?xml version="1.0" encoding="ISO-8859-1" ?>
<site_entries>
<entry>
<id><![CDATA[1]]></id>
</entry>
<entry>
<id><![CDATA[2]]></id>
</entry>
</site_entries>

b.xml

<?xml version="1.0" encoding="ISO-8859-1" ?>
<site_entries>
<entry>
<id><![CDATA[2]]></id>
</entry>
<entry>
<id><![CDATA[3]]></id>
</entry>
</site_entries>