Simple logging code snippet

gistfile1.c

#include <windows.h>
#include <stdio.h>
#include <stdarg.h>

static CRITICAL_SECTION crit;

void log_init()
{
    static volatile LONG done = 0;
    if (done == 0) {
        if (InterlockedIncrement(&done) == 1) {
            InitializeCriticalSection(&crit);
        }
    }
}

void log_on(const char *format, ...)
{
    FILE *fp;
    va_list va;
    
    log_init();
    EnterCriticalSection(&crit);
    fp = fopen("logfile.txt", "a+");
    if (fp != NULL) {
        va_start(va, format);
        vfprintf(fp, format, va);
        fputs("\n", fp);
        va_end(va);
        fclose (fp);
    }
    LeaveCriticalSection(&crit);
}