Static library

bad.cpp

// IIRC it's a bit vague when this DataRef registers and gets destructed
PPL::DataRef<std::string> sim_build{"sim/version/sim_build_string"};

PLUGIN_API int XPluginStart(char *outName, char *outSig, char *outDesc) {
  char name[] = "BadExample";
  strcpy(outName, name); strcpy(outSig, name); strcpy(outDesc, name);

  return 1;
}

PLUGIN_API void XPluginStop() {}
PLUGIN_API void XPluginDisable() {}
PLUGIN_API int XPluginEnable() { 
  XPLMSpeakString(sim_build.c_str());
  return 1;
}
PLUGIN_API void XPluginReceiveMessage(XPLMPluginID, long, void *) {}

better.cpp

#include <memory>

std::unique_ptr<PPL::DataRef<std::string>> sim_build;

PLUGIN_API int XPluginStart(char *outName, char *outSig, char *outDesc) {
  char name[] = "BetterExample";
  strcpy(outName, name); strcpy(outSig, name); strcpy(outDesc, name);
  
  // With this pattern, the dataref is only registered when XPluginStart is called
  sim_build = std::make_unique<PPL::DataRef<std::string>>("sim/version/sim_build_string");
  return 1;
}

PLUGIN_API void XPluginStop() {}
PLUGIN_API void XPluginDisable() {}
PLUGIN_API int XPluginEnable() {
  // there's probably a better way to get the string out of the DataRef out of the unique_ptr
  std::string s{*foo.get()};
  XPLMSpeakString(s.c_str());
 return 1;
}
PLUGIN_API void XPluginReceiveMessage(XPLMPluginID, long, void *) {}

normal.cpp

#include <memory>

// more usually, the datarefs I'm accessing are part of a class or struct that does something
struct Foo {
  PPL::DataRef<std::string> sim_build{"sim/version/sim_build_string"};
  PPL::DataRef<int> xpdr_blink{"sim/cockpit/radios/transponder_code"};
  PPL::DataRef<float> ias_kts{
      "sim/cockpit2/gauges/indicators/airspeed_kts_pilot"};
  void speak() {
    std::stringstream s;
    s << ias_kts << "kts, " << std::string(sim_build);
    XPLMSpeakString(s.str().c_str());
  }
};

std::unique_ptr<Foo> foo;

PLUGIN_API int XPluginStart(char *outName, char *outSig, char *outDesc) {
  char name[] = "BetterExample";
  strcpy(outName, name); strcpy(outSig, name); strcpy(outDesc, name);
 
  // this makes it much cleaner to create everything
  foo = std::make_unique<Foo>();

  return 1;
}

PLUGIN_API void XPluginStop() {}
PLUGIN_API void XPluginDisable() {}
PLUGIN_API int XPluginEnable() {
  foo->speak();
  return 1;
}
PLUGIN_API void XPluginReceiveMessage(XPLMPluginID, long, void *) {}