IRIS supports of Python and C++

You are correct that callin is not a replacement for the C++ binding. Callin is a lower-level API that only works for a local instance. The C++ binding has two flavors: the light C++ binding (LCB), which depends on callin, and the full C++ binding, which depends on the ODBC driver.

It's not clear to me from your questions how you're currently using C++. Do you actually have an existing C++ binding application, or are you writing something new with a requirement to use C++? I suggest that you get in touch with your friendly InterSystems representative in Support or Sales Engineering to help you find the best path forward.

That said, I was curious about whether the C++ binding from Caché can be used with InterSystems IRIS. Although I've never used this API on purpose, I was able to get it working after a fashion with a few modifications. I presume this is not supported by InterSystems, and I would hesitate to use it in production. The following overview describes my experiment using the C++ binding SDK from a Caché 2018.1.4 kit for lnxrhx64 with the Community edition of IRIS 2020.3.0 in a container. Apologies for any copy-paste mistakes. I started this on a lark, and didn't take very good notes.

I installed g++, make, and vim in the container:

$ docker exec -it --user root cppbind bash
root:/home/irisowner# apt update && apt install -y g++ make vim
...

I extracted cppsdk-lnxrhx64.tar.gz, and found that the C++ binding uses dlsym() and dlopen() to call entry points in the ODBC driver library. (Search for the init_pfn macro in odbc_common.cpp.) These are still present in the IRIS library, as you can see with the nm command:

$ docker exec -it cppbind bash
irisowner:~$ nm /usr/irissys/bin/libirisodbciw35.so |grep cpp_
000000000005cf90 T cpp_binding_alloc_messenger
000000000005dd40 T cpp_binding_clear_odbc_cache
...

I changed the ODBCLIBNAME symbol in libcppbind.mak from the libcacheodbciw Caché driver library to the libirisodbciw35 IRIS driver library.

I changed the Caché "CacheUni" symbols to the IRIS "ServerUni" symbols. For those three symbols, instead of

*((void**)(&(func))) = dlsym(dll_handle, #func);

You want something like this, where name is the new name of the symbol in the IRIS driver:

*((void**)(&(func))) = dlsym(dll_handle, #name);

I did the same for the ODBC 2.x SQLColAttributesW() function, which has been replaced by the ODBC 3.x SQLColAttributeW() function.

I fixed an apparent bug in obj_types.h by marking get_cs_handle() const and cs_handle mutable. I didn't spend much time investigating, so I'm not certain that this is the best fix.

I then built the C++ binding:

irisowner:~/dev/cpp/src/modules/cpp/lnxrhx64$ make libcppbind.so

It appears that the cpp_generator utility is only shipped as a binary, which obviously doesn't have any of these changes, so it won't work with an IRIS driver library. However, I was able to do a simple test using Dyn_obj:

#include <iostream>
#include "cppbind.h"

using namespace InterSystems;

int
main()
{
    auto conn = tcp_conn::connect(
        "localhost[1972]:USER", "_system", "SYS");
    Database db{conn};
    d_string res;
    Dyn_obj::run_class_method(&db, L"%SYSTEM.Util", L"CreateGUID",
        nullptr, 0, &res);
    std::cout << res.value() << std::endl;

    return 0;
}

I compiled and ran the test program like so:

$ docker exec -it cppbind bash
irisowner:~$ g++ -o cppbindtest cppbindtest.cpp -I dev/cpp/include \
    -L dev/cpp/src/kit/lnxrhx64/release/bin -lcppbind
irisowner:~$ export LD_LIBRARY_PATH=/home/irisowner/dev/cpp/src/kit/lnxrhx64/release/bin:/usr/irissys/bin
irisowner:~$ ./cppbindtest 
7325F26A-21E2-11EB-BB36-0242AC110002