localtime在多线程中的问题

碰到一个奇怪的问题，通过localtime生成本地日期时间打日志，结果日志会出现非北京时间，好奇去查了一个，结果发现此函数是非线程安全函数，原来代码如下：

int32_t utc2datetime(uint32_t utctime, SVC_TIME* out_pTime)
{
	time_t rawtime;
	struct tm * p;
	rawtime = utctime;
	p = localtime(&rawtime);
	out_pTime->unYear = (uint32_t)(1900 + p->tm_year);
	out_pTime->unMonth = (uint16_t)(1 + p->tm_mon);
	out_pTime->unDay = (uint16_t)p->tm_mday;
	out_pTime->unHour = (uint16_t)p->tm_hour;
	out_pTime->unMinute = (uint16_t)p->tm_min;
	out_pTime->unSecond = (uint16_t)p->tm_sec;
	out_pTime->unWeek = (uint16_t)p->tm_wday;
	return 0;
}

localtime，用来获取系统时间，原型在time.h头文件中，定义如下：

struct tm *localtime(const time_t *timep);

在实际应用中，用了2个线程一个统计，一个日志使用此函数，结果就会出现读出的SVC_TIME有的是北京时间，有的是-8小时的时间，需要使用线程安全函数，localtime_r和localtime_s，localtime_r是linux下线程安全函数，localtime_s是windows下线程安全函数，定义分别如下：

struct tm *localtime_r( const time_t *timer, struct tm *_tm );

errno_t localtime_s(struct tm* _tm,const time_t *time);

注意：localtime_r和localtime_s的参数是相反的。

改动原来的函数如下就可以正常使用了：

int32_t utc2datetime(uint32_t utctime, SVC_TIME* out_pTime)
{
	time_t rawtime;
	struct tm  tm = {0};
	rawtime = utctime;
#if defined(_WIN32) || defined(_WIN64)
	localtime_s(&tm, &rawtime);
#else
	localtime_r(&rawtime, &tm);
#endif
	out_pTime->unYear = (uint32_t)(1900 + tm.tm_year);
	out_pTime->unMonth = (uint16_t)(1 + tm.tm_mon);
	out_pTime->unDay = (uint16_t)tm.tm_mday;
	out_pTime->unHour = (uint16_t)tm.tm_hour;
	out_pTime->unMinute = (uint16_t)tm.tm_min;
	out_pTime->unSecond = (uint16_t)tm.tm_sec;
	out_pTime->unWeek = (uint16_t)tm.tm_wday;
	return 0;
}