Log to file and log to syslog on Linux on C

logging_Linux.c

#include <stdarg.h>
#include <syslog.h>
#include <time.h>

/**
 * \brief Log levels. Used to control applications's verbosity.
 *
 * Verbosity is as follows: LOG_CRITICAL_ERROR is least verbose, 
 * LOG_EVENT is the most verbose log level.
 */
typedef enum {
	/** \brief A flag to indicate that _critical_ error message is logged. */
	LOG_CRITICAL_ERROR,
	/** \brief A flag to indicate that error message is logged. */
	LOG_ERROR,
	/** \brief A flag to indicate that warning message is logged. */
	LOG_WARNING,
	/** \brief A flag to indicate that some diagnostic message is logged. */
	LOG_INFO,
	/** \brief A flag to indicate that some message is logged to special log */
	LOG_SPECIAL
} log_e;

log_e g_log_verbosity = LOG_WARNING;

static const char* g_log_message_names[] =
{
	"CRITICAL ERROR",
	"ERROR",
	"WARNING",
	"INFO"
};

void log(log_e level, char* format, ...)
{
	FILE *stream;
    
	if (level == LOG_SPECIAL) {
	    char buf[300];
	    sprintf(buf, "APP: ");
	    va_list argptr;
	    va_start(argptr, format);
	    vsnprintf(&buf[strlen(buf)], sizeof(buf - strlen(buf)), format, argptr);
	    va_end(argptr);
	    openlog ("AppName", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_LOCAL2);
	    syslog (LOG_INFO, buf);
	}
	if (level > g_log_verbosity)
		return;

    if (g_log_verbosity == LOG_SPECIAL) {
        char log_name[50];
        if (strlen(username) > 0)
            snprintf(log_name, sizeof(log_name), "%s.log", username);
        else
            return;
        stream = fopen(log_name, "a+");
        if (stream == NULL) {
            perror("Writing to log file");
            return;
        }
    } else
        stream = stderr;

    time_t sec_since_Epoch = time(NULL);
    struct tm *date_time = localtime(&sec_since_Epoch);

	fprintf(stream, "%02d:%02d:%02d %s: ", date_time->tm_hour, date_time->tm_min,
			date_time->tm_sec, g_log_message_names[level]);

	va_list argptr;
	va_start(argptr, format);
	vfprintf(stream, format, argptr);
	va_end(argptr);

	fprintf(stream, "\n");
    
    if ((g_log_verbosity == LOG_SPECIAL) && (stream != NULL)) {
        int status = fclose(stream);
        if (status != 0) {
            perror("Closing log file");
            return;
        }
    }
}

void set_log_verbosity(log_e level)
{
	g_log_verbosity = level;
}