First C++ Apache Module

Foo.h

#pragma once

#include <string>
using std::string;

#include "http_protocol.h"

class Foo {
    public:
        int RunHandler(request_rec *req) {
            if (!req->handler || module_name != req->handler) return DECLINED;

            ap_rputs(message.c_str(), req);
            return OK;
        }
    private:
        string module_name = "foo";
        string message = "Hello world from " + module_name;
};

httpd.conf

LoadFile /usr/lib/x86_64-linux-gnu/libstdc++.so.6
LoadModule foo_module modules/mod_foo.so
<Location /foo>
    SetHandler foo
</Location>

make

vishalj@dreamland:~/src/foo$ make reload
make[1]: Entering directory '/home/vishalj/src/foo'
/home/vishalj/www/build/libtool --silent --mode=compile g++ -std=c++14 -DLINUX -D_REENTRANT -D_GNU_SOURCE -I/home/vishalj/www/include -I. -I/home/vishalj/src/httpd/mybuild/srclib/apr/include -I/home/vishalj/src/httpd/srclib/apr/include -prefer-pic -c mod_foo.cpp && touch mod_foo.slo
/home/vishalj/www/build/libtool --silent --mode=link gcc -std=gnu99 -g -O2 -pthread -o mod_foo.la -rpath /home/vishalj/www/modules -module -avoid-version mod_foo.lo
/home/vishalj/www/build/libtool --silent --mode=install install mod_foo.la /home/vishalj/www/modules/
make[1]: Leaving directory '/home/vishalj/src/foo'
/home/vishalj/www/build/libtool --silent --mode=install install mod_foo.la /home/vishalj/www/modules/
~/www/bin/apachectl restart
vishalj@dreamland:~/src/foo$

Makefile

##
##  Makefile -- Build procedure for sample foo Apache module
##  Autogenerated via ``apxs -n foo -g''.
##
builddir=.
top_srcdir=/home/vishalj/www
top_builddir=/home/vishalj/www
include /home/vishalj/www/build/special.mk

CXX=g++
CXXFLAGS=-std=c++14

#   the used tools
APACHECTL=~/www/bin/apachectl

#   additional defines, includes and libraries
#DEFS=-Dmy_define=my_value
#INCLUDES=-Imy/include/dir
#LIBS=-Lmy/lib/dir -lmylib

#   the default target
all: local-shared-build

#   install the shared object file into Apache 
install: install-modules-yes
#   cleanup
clean:
    -rm -f mod_foo.o mod_foo.lo mod_foo.slo mod_foo.la

#   simple test
test: reload
    lynx -mime_header http://localhost/foo

#   install and activate shared object by reloading Apache to
#   force a reload of the shared object file
reload: install restart

#   the general Apache start/restart/stop
#   procedures
start:
    $(APACHECTL) start
restart:
    $(APACHECTL) restart
stop:
    $(APACHECTL) stop

mod_foo.cpp

#include <memory>

#include "Foo.h"
#include "http_config.h"

auto foo = std::make_unique<Foo>();

extern "C" {
    void foo_hooks(apr_pool_t* pool);
    module AP_MODULE_DECLARE_DATA foo_module = {
        STANDARD20_MODULE_STUFF,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        foo_hooks
    };
};

// Apache callback to register our hooks
void foo_hooks(apr_pool_t* pool) {
    ap_hook_handler(
            [](request_rec *req) {
                return foo->RunHandler(req);
            },
            NULL, NULL, APR_HOOK_MIDDLE);
}

Thanks!

I just needed to adjust the httpd.conf to add the complete path of the generated shred object, which was /usr/lib/apache2/modules/mod_foo.so , I also moved the httpd.conf to /etc/apache2/conf-available/foo.conf and then enabled it sudo a2enconf foo.
All worked perfectly!