以下似乎很奇怪。我处于夏令时的中央时间，应该与UTC相差-5。当我输出struct tm对象的字符串表示时，它看起来是正确的。但是当我将struct tm转换为time_t并且我查看这些值时，我得到21600的差异，即6小时（21600秒/ 60/60 = 6小时）。我希望它是5个小时。
我在Ubuntu 12.04上运行Gcc 4.8.2。
9 time_t t1 = time(nullptr);
10 time_t t2 = t1;
11
12 char buf1[64];
13 char buf2[64];
14
15 tm utcTm, localTm;
16 tm* tmp;
17
18 tmp = gmtime(&t1);
19 utcTm = *tmp;
20
21 tmp = localtime(&t2);
22 localTm = *tmp;
23
24 strftime(buf1, 64, "%c %Z", &utcTm);
25 strftime(buf2, 64, "%c %Z", &localTm);
26
27 cout << "UTC: " << buf1 << endl;
28 cout << "local: " << buf2 << endl;
29
30 cout << "Is DST? " << utcTm.tm_isdst << " " << localTm.tm_isdst << endl;
31
32 time_t t3 = mktime(&utcTm);
33 time_t t4 = mktime(&localTm);
34
35 cout << "UTC: " << t3 << " Local: " << t4 << " Diff: " << (t3 - t4) << endl;
36 cout << "Orig UTC: " << t3 << " Orig Local: " << t4 << " Diff: " << (t3 - t4) << endl;
输出：
UTC：星期一2月2日19:05:23 GMT
local：Mon Jun 2 14:05:23 CDT
是夏令时吗？ 0 1
UTC：1401757523 Local：1401735923 Diff：21600