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