Added errno description to sdlog exception strings

include/spdlog/details/os.h

@@ -10,6 +10,7 @@
 #include <ctime>
 #include <functional>
 #include <string>
+#include <string.h>
 
 #ifdef _WIN32
 
@@ -27,12 +28,16 @@
 #endif
 
 #elif __linux__
+
 #include <sys/syscall.h> //Use gettid() syscall under linux to get thread id
 #include <sys/stat.h>
 #include <unistd.h>
 #include <chrono>
+
 #else
+
 #include <thread>
+
 #endif
 
 namespace spdlog
@@ -246,6 +251,30 @@ inline std::string filename_to_str(const filename_t& filename)
 }
 #endif
 
+
+// Return errno string (thread safe)
+inline std::string errno_str(int err_num)
+{	
+	char buf[256];	
+	constexpr auto buf_size = sizeof(buf);
+			
+#ifdef _WIN32		
+	if(strerror_s(buf, buf_size, err_num) == 0)
+		return std::string(buf);
+	else
+		return "Unkown error";
+
+#elif (_POSIX_C_SOURCE >= 200112L) && ! _GNU_SOURCE // posix version		
+	if (strerror_r(err_num, buf, buf_size) == 0)
+		return std::string(buf);
+	else
+		return "Unkown error";
+
+#else  // gnu version (might not use the given buf, so its retval pointer must be used)
+	return std::string(strerror_r(err_num, buf, buf_size));
+#endif		
+}
+
 } //os
 } //details
 } //spdlog