Based on an Insomniac's Engine programmer's blog, this is a trick I learned from him.

c_cpp_lambda_callback.cpp

#include <iostream>
#include <utility>

void callback_test(void* userdata, void* path) {
 	 std::cout << "Callback function called with path: " 
               << static_cast<const char*>(path)
               << " and userdata: "
               << static_cast<const char*>(userdata) << std::endl;
}

typedef void (*ResourceLoadCB) (void*, void*);

struct LoadDesc
{
  const char* path;
  void* userdata;
  ResourceLoadCB callback;
};

// Function to load a resource
bool load_resource(LoadDesc* loaddesc) {
    if (loaddesc->path != nullptr) {
        loaddesc->callback(loaddesc->userdata, (void*)loaddesc->path);
        return true; // Indicate successful execution
    }
    return false; // Indicate failure
}

template <typename Fn>
bool load_resource(LoadDesc* loaddesc, Fn func) {
	auto closure = [](void* userdata, void* path) {
    	// cast the Fn from userdata
        Fn* funcPtrToLambda = static_cast<Fn*>(userdata);
        // userdata of the Fn is implicit we call this function as a deferred call inside another lambda that mathced our signature
        (*funcPtrToLambda)(path);
    };
    loaddesc->userdata = &func;
    loaddesc->callback = closure;
    
    return load_resource(loaddesc);
}

int main() {
    LoadDesc desc;
    desc.path = "/path/to/";
    desc.userdata = (void*)"filename.txt";
    desc.callback = callback_test;

    // Pass the address of `desc` to `load_resource`
    if (load_resource(&desc)) {
        std::cout << "Resource loaded successfully." << std::endl;
    } else {
        std::cout << "Failed to load resource." << std::endl;
    }


    // Exampele 2: using lambda
    const char* new_ext = "buffer.asset";
    auto loadCB = [new_ext](void* path) {
        std::cout << "Lambda Callback function called with path: " 
               << static_cast<const char*>(path)
               << " and userdata: "
               << static_cast<const char*>(new_ext) << std::endl;

    };

    LoadDesc loadcbDesc;
    loadcbDesc.path = "path/to/CB/";

if (load_resource(&loadcbDesc, loadCB)) {
        std::cout << "Resource loaded successfully." << std::endl;
    } else {
        std::cout << "Failed to load resource." << std::endl;
    }
    return 0;
}