c – 为什么mktime()改变了我的tm结构的年份？

概述我读了两个字符串,包括年份,朱利安日(年),小时,分钟和观察. 我使用sscanf将相关变量拉出来： sscanf(tide_str1.c_str(), "%d %d %d %d %Lf", &y1, &j1, &h1, &m1, &obs1);sscanf(tide_str2.c_str(), "%d %d %d %d %Lf", &y2, &j2, &h2, &m2, &obs2); 对于此 我读了两个字符串,包括年份,朱利安日(年),小时,分钟和观察.

我使用sscanf将相关变量拉出来：

sscanf(tIDe_str1.c_str(),"%d %d %d %d %Lf",&y1,&j1,&h1,&m1,&obs1);sscanf(tIDe_str2.c_str(),&y2,&j2,&h2,&m2,&obs2);

对于此特定数据集,值为2011 083 23 22 1.1

然后我创建并填充一个tm结构,运行mktime,在两天之间的cout调用,它从083变为364.

int y1=2011,j1=83,h1=23,m1=22;struct tm time_struct = {0,0},*time_ptr = &time_struct;time_t tv_min;time_struct.tm_year = y1 - 1900;time_struct.tm_yday = j1;cout << time_struct.tm_yday << endl;time_struct.tm_hour = h1;time_struct.tm_min = m1;time_struct.tm_isdst = -1;cout << time_struct.tm_yday << endl;tv_min = mktime(time_ptr);cout << time_struct.tm_yday << endl;

这是为什么？是因为tm_mday和tm_mon设置为0？我最初尝试不将它全部初始化为零,但随后mktime返回-1.如果我只知道年份而不是月份和月份,我应该做些什么呢？

解决方法 mktime()正在做它应该做的事情.

引用C标准：

The mktime function converts the broken-down time,expressed as
local time,in the structure pointed to by timeptr into a calendar
time value with the same enCoding as that of the values returned by
the time function. The original values of the tm_wday and
tm_yday components of the structure are ignored,and the original values of the other components are not restricted to the ranges
indicated above. On successful completion,the values of the
tm_wday and tm_yday components of the structure are set appropriately,and the other components are set to represent the
specifIEd calendar time,but with their values forced to the ranges
indicated above; the final value of tm_mdayis not set until tm_mon
and tm_year are determined.

mktime()可以从其他成员计算tm_mday和tm_yday的值;它不是为了计算这些字段中其他成员的值而设计的.

但是,您可以做的是使用超出范围的值初始化struct tm.例如,如果您希望tm_yday为200(一年中的第200天),则可以初始化表示1月200日的结构tm.然后mktime()会将其标准化为正确的日期,产生一个time_t值,然后您可以将其提供给gmtime()或localtime().

这是一个简单的例子：

#include <iostream>#include <ctime>int main(){    struct tm t = { 0 };    t.tm_sec = t.tm_min = t.tm_hour = 0; // mIDnight    t.tm_mon = 0;                        // January    t.tm_year = 2012 - 1900;    t.tm_isdst = -1;                     // unkNown    t.tm_mday = 200;                     // January 200th?    time_t when = mktime(&t);    const struct tm *norm = localtime(&when);   // normalized time    std::cout << "month=" << norm->tm_mon << ",day=" << norm->tm_mday << "\n";    std::cout << "The 200th day of 2012 starts " << asctime(norm);}

输出是：

month=6,day=18The 200th day of 2012 starts Wed Jul 18 00:00:00 2012

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