写日志 可变参数

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <stdlib.h>
#include <stdarg.h>
using namespace std;

int logfile(const char * format, ...)
{
    FILE *logfile;
    logfile=fopen("1.txt","a+");
    va_list arg_ptr;
    va_start(arg_ptr, format);
    int nWrittenBytes = vfprintf(logfile, format, arg_ptr);
    va_end(arg_ptr);
    return nWrittenBytes;
}
int main()
{
    logfile("%s logged out.","124");
}