Keep unused exported functions from being stripped by linker, useful for linking static libraries that have unused exported functions targeted for C# P/Invoke marshaling or misc purposes

1_export.h

#pragma once

// LINKER_INCLUDE_UNUSED: Forces linker to keep unused functions that were declared elsewhere
// LINKER_KEEP_UNUSED: Forces linker to keep unused functions that are delcared within the current file

#define EXPORT extern "C" _declspec(dllexport)

#if defined(LINKER_INCLUDE_UNUSED)
    #if defined(_WIN64)
        #define LINKER_KEEP(s) EXPORT __pragma(comment (linker, "/export:"#s))
    #elif defined(_WIN32)
        #define LINKER_KEEP(s) EXPORT __pragma(comment (linker, "/export:_"#s))
    #endif
#elif defined(LINKER_KEEP_UNUSED)
    #if defined(_WIN64)
        #define LINKER_KEEP(s) EXPORT __pragma(comment (linker, "/include:"#s))
    #elif defined(_WIN32)
        #define LINKER_KEEP(s) EXPORT __pragma(comment (linker, "/include:_"#s))
    #endif
#endif

#define EXPORT_KEEP(RET, NAME, ...) LINKER_KEEP(NAME) RET NAME(__VA_ARGS__)

2_example.cpp

#include <cstdio>  // printf

#define LINKER_KEEP_UNUSED
#include "export.h"

EXPORT_KEEP(void, myFn1);
void myFn1() {
    printf("HELLO!\n");
}

EXPORT_KEEP(void, myFn2, int);
void myFn2(int a) {
    printf("NUMBER: %d\n", a);
}