A quick example showing loading CLR via native code

clr_via_native.c

#include "stdafx.h"

int main()
{
	ICLRMetaHost *metaHost = NULL;
	IEnumUnknown *runtime = NULL;
	ICLRRuntimeInfo *runtimeInfo = NULL;
	ICLRRuntimeHost *runtimeHost = NULL;
	IUnknown *enumRuntime = NULL;
	LPWSTR frameworkName = NULL;
	DWORD bytes = 2048, result = 0;
	HRESULT hr;

	printf("CLR via native code.... @_xpn_\n\n");

	if (CLRCreateInstance(CLSID_CLRMetaHost, IID_ICLRMetaHost, (LPVOID*)&metaHost) != S_OK) {
		printf("[x] Error: CLRCreateInstance(..)\n");
		return 2;
	}

	if (metaHost->EnumerateInstalledRuntimes(&runtime) != S_OK) {
		printf("[x] Error: EnumerateInstalledRuntimes(..)\n");
		return 2;
	}

	frameworkName = (LPWSTR)LocalAlloc(LPTR, 2048);
	if (frameworkName == NULL) {
		printf("[x] Error: malloc could not allocate\n");
		return 2;
	}

	// Enumerate through runtimes and show supported frameworks
	while (runtime->Next(1, &enumRuntime, 0) == S_OK) {
		if (enumRuntime->QueryInterface<ICLRRuntimeInfo>(&runtimeInfo) == S_OK) {
			if (runtimeInfo != NULL) {
				runtimeInfo->GetVersionString(frameworkName, &bytes);
				wprintf(L"[*] Supported Framework: %s\n", frameworkName);
			}
		}
	}

	// For demo, we just use the last supported runtime
	if (runtimeInfo->GetInterface(CLSID_CLRRuntimeHost, IID_ICLRRuntimeHost, (LPVOID*)&runtimeHost) != S_OK) {
		printf("[x] ..GetInterface(CLSID_CLRRuntimeHost...) failed\n");
		return 2;
	}

	if (runtimeHost == NULL || bytes == 0) {
		wprintf(L"[*] Using runtime: %s\n", frameworkName);
	}

	// Start runtime, and load our assembly
	runtimeHost->Start();

	printf("[*] ======= Calling .NET Code =======\n\n");
	if (runtimeHost->ExecuteInDefaultAppDomain(
			L"myassembly.dll",
			L"myassembly.Program",
			L"test",
			L"argtest",
			&result
	) != S_OK) {
		printf("[x] Error: ExecuteInDefaultAppDomain(..) failed\n");
		return 2;
	}
	printf("[*] ======= Done =======\n");
	

    return 0;
}

#include <metahost.h>
#pragma comment(lib, "mscoree.lib")

int main()
{
ICLRMetaHost* metaHost = NULL;
ICLRRuntimeInfo* runtimeInfo = NULL;
ICLRRuntimeHost* runtimeHost = NULL;

if (CLRCreateInstance(CLSID_CLRMetaHost, IID_ICLRMetaHost, (LPVOID*)&metaHost) == S_OK)
    if (metaHost->GetRuntime(L"v4.0.30319", IID_ICLRRuntimeInfo, (LPVOID*)&runtimeInfo) == S_OK)
        if (runtimeInfo->GetInterface(CLSID_CLRRuntimeHost, IID_ICLRRuntimeHost, (LPVOID*)&runtimeHost) == S_OK)
            if (runtimeHost->Start() == S_OK)
      {    
    DWORD pReturnValue;
    runtimeHost->ExecuteInDefaultAppDomain(L"C:\\random.dll", L"dllNamespace.dllClass", L"ShowMsg", L"It works!!", &pReturnValue);

    runtimeInfo->Release();
    metaHost->Release();
    runtimeHost->Release();
            }
return 0;

}
#https://www.unknowncheats.me/forum/general-programming-and-reversing/332825-inject-net-dll-using-clr-hosting.html