C++使用localtime函数需要注意的地方http://blog.csdn.net/shellching/article/details/8114266
2015-07-29 09:24
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C++使用localtime函数需要注意的地方
分类: C/C++2012-10-2611:14 6974人阅读 评论(1) 收藏 举报
在处理时间时用到了localtime这个函数,将一个UTC时间转为本地时间:
[cpp] view
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#include <time.h>
time_t tmNow = time(NULL);
tm *ptmNow = localtime(&tmNow); //从tm结构体中可以取到年月日时分秒等值。
这里localtime返回了一个tm指针,空间是由localtime自己控制的,所以如果连续调用这个函数会有问题。
很多时候我们会同时处理两个时间,例如表示时间段的【起始时间】【结束时间】,代码如下:
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time_t tmBegin = 1351118531; //2012-10-25 06:42:11
time_t tmEnd = 1351218731; //2012-10-26 10:32:11
tm* ptmBegin = localtime(&tmBegin );
tm* ptmEnd = localtime(&tmEnd );//第二次调用会修改上次调用的tm结构体,若上次的数据未保存则会丢失
//tm* ptm3 = gmtime(&tmEnd ); //效果同上条语句,也会重写之前的数据
char ctmBegin1[26], ctmEnd[26];
strftime(ctmBegin, 26, "%Y%m%d%H%M%S", ptmBegin); //这里输出的将是tmEnd的时间值
strftime(ctmEnd, 26, "%Y%m%d%H%M%S", ptmEnd);
/*MSDN中有相关说明:
Both the 32-bit and 64-bit versions ofgmtime, mktime, mkgmtime, and localtimeall
use a single tm structure per thread for the conversion. Each call to one of these
routines destroys the result of the previous call.
*/
所以要记住,一旦调用了localtime函数,应该马上取出tm结构中的内容:
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time_t tmBegin = 1351118531; //2012-10-25 06:42:11
time_t tmEnd = 1351218731; //2012-10-26 10:32:11
char ctmBegin1[26], ctmEnd[26];
tm* ptmBegin = localtime(&tmBegin );
strftime(ctmBegin, 26, "%Y%m%d%H%M%S", ptmBegin);
tm* ptmEnd = localtime(&tmEnd );
strftime(ctmEnd, 26, "%Y%m%d%H%M%S", ptmEnd);
//tm* ptm3 = gmtime(&tmEnd );
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