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");}