How to call a method within a Function block in Twincat ST through C++ ADS code?

That is I want to call a method, suppose TestMethod of FB_CALCULATOR, from C++ code using the ADS libraries. I'm unable to find examples for this in C++. The available examples seem to be only for C#, and these functions do not exist in their C++ ADS Libraries. I have tried going through Beckhoff infosys but haven't found anything useful for this in C++.

This is lifted straight from https://github.com/Beckhoff/ADS/issues/131:

typedef struct
{
    unsigned long a;
    unsigned long b;
} MethodParameters;

// ...

long nErr, nPort;
AmsAddr Addr;
PAmsAddr pAddr = &Addr;
ULONG lHdlVar, rValue;
char szVar[] = {"MAIN.foo#DoAdd"};
MethodParameters params;

// ...

nPort = AdsPortOpen();
nErr = AdsGetLocalAddress(pAddr);
if (nErr)
{
    cerr << "Error: AdsGetLocalAddress: " << nErr << '\n';
}

pAddr->port = 851;

nErr = AdsSyncReadWriteReq(pAddr, ADSIGRP_SYM_HNDBYNAME, 0x0, sizeof(lHdlVar), &lHdlVar, sizeof(szVar), szVar);
if (nErr)
{
    cerr << "Error: AdsSyncReadWriteReq: " << nErr << '\n';
}

params.a = 5;
params.b = 5;

nErr = AdsSyncReadWriteReq(pAddr, ADSIGRP_SYM_VALBYHND, lHdlVar, sizeof(rValue), &rValue, sizeof(params), &params);
if (nErr)
{
    cerr << "Error: AdsSyncReadWriteReq: " << nErr << '\n';
}

cout << "rValue: " << rValue;

nErr = AdsSyncWriteReq(pAddr, ADSIGRP_SYM_RELEASEHND, 0, sizeof(lHdlVar), &lHdlVar);
if (nErr)
{
    cerr << "Error: AdsSyncWriteReq: " << nErr << '\n';
}

nErr = AdsPortClose();
if (nErr)
{
    cerr << "Error: AdsPortClose: " << nErr << '\n';
}