EventManager: Add optional debug printing

README.md

@@ -110,6 +110,10 @@ for(size_t i = 0; i < messageCount; i++) {
 icsneo_closeDevice(myDevice);
 ```
 
+### Debugging
+
+To enable debug printing set the `LIBICSNEO_PRINT_EVENTS` environmental variable to the desired `APIEvent::Severity` level, all `Event`s greater than or equal to that level will be printed to stderr. For example, to print all warnings and errors: `LIBICSNEO_PRINT_EVENTS=32`.
+
 ## Building from Source
 ### FTD3XX
 Some devices require FTD3XX for USB communication so the [FTDI D3XX library](https://ftdichip.com/drivers/d3xx-drivers/) will be automatically downloaded and included. If you would like to use a system copy of D3XX instead you can set `FTD3XX_ROOT` to the path containing `f3d3xx.h` (`-DFTD3XX_ROOT=<path to directory containing ftd3xx.h>`).

api/icsneocpp/eventmanager.cpp

@@ -1,5 +1,8 @@
 #include "icsneo/api/eventmanager.h"
 #include <memory>
+#include <optional>
+#include <iostream>
+#include <cstdlib>
 
 using namespace icsneo;
 
@@ -33,6 +36,25 @@ void EventManager::cancelErrorDowngradingOnCurrentThread() {
 void EventManager::add(APIEvent event) {
 	if(destructing)
 		return;
+	static const auto printLevel = []() -> std::optional<uint8_t> {
+		#ifdef _MSC_VER
+		#pragma warning(push)
+		#pragma warning(disable : 4996)
+		#endif
+		const auto level = std::getenv("LIBICSNEO_PRINT_EVENTS");
+		#ifdef _MSC_VER
+		#pragma warning(pop)
+		#endif
+		if(!level)
+			return std::nullopt;
+		try {
+			return (uint8_t)std::stoi(level);
+		} catch (std::invalid_argument const&) {
+			return std::nullopt;
+		}
+	}();
+	if(printLevel && (uint8_t)event.getSeverity() >= *printLevel)
+		std::cerr << event.describe() << std::endl;
 	if(event.getSeverity() == APIEvent::Severity::Error) {
 		// if the error was added on a thread that downgrades errors (non-user thread)
 		std::lock_guard<std::mutex> lk(downgradedThreadsMutex);