Daily log files with Loguru

daily_loguru.cpp

// The first 10 bytes of message.preamble is the current date in YYYY-MM-DD.
#define DATE_LEN 10

struct DailyLogger
{
	FILE* file           = nullptr;
	char  date[DATE_LEN] = { 0 };
};

void daily_log(void* user_data, const loguru::Message& message)
{
	DailyLogger* logger = reinterpret_cast<DailyLogger*>(user_data);

	if (strncmp(logger->date, message.preamble, DATE_LEN) != 0) {
		// A new day (or first time we ever log)
		fclose(logger->file);
		char filename[15];
		sprintf(filename, "%.*s.log", DATE_LEN, message.preamble);
		logger->file = fopen(filename, "w");
		memcpy(logger->date, message.preamble, DATE_LEN);
	}

	fprintf(logger->file, "%s%s%s%s\n", message.preamble, message.indentation, message.prefix, message.message);
	fflush(logger->file);
}

void daily_close(void* user_data)
{
	DailyLogger* logger = reinterpret_cast<DailyLogger*>(user_data);
	fclose(logger->file);
	delete logger;	
}

...

loguru::add_callback("daily", daily_log, new DailyLogger, daily_close);