Question

我是一名初学者，我试图计算两个日期之间的天数，但我不清楚时间。我可以指出我的错误吗？因为打印后sec = 0。谢谢。

#include <stdio.h>
#include <time.h>

main(){



    double sec;

    struct tm BD;
        BD.tm_mday;        
        BD.tm_mon;         
        BD.tm_year;

    struct tm KT;
        KT.tm_mday;        
        KT.tm_mon;         
        KT.tm_year;

    printf("Start date: ");
    scanf("%d %d %d",&BD.tm_mday,&BD.tm_mon,&BD.tm_year);

    printf("End date: ");
    scanf("%d %d %d",&KT.tm_mday,&KT.tm_mon,&KT.tm_year);

    sec = difftime(mktime(&KT),mktime(&BD));

    printf("%f",sec); 

// date= sec/86400 //

    return 0;
}

Answer 1

请尝试这个例子。您需要将时钟设置为午夜并将结果舍入为整数，然后计算是正确的：

#include <stdio.h>
#include <time.h>
int main () {
    struct tm start_date;
    struct tm end_date;
    time_t start_time, end_time;
    double seconds;
    printf("Start date: ");
    scanf("%d %d %d",&start_date.tm_mday ,&start_date.tm_mon,&start_date.tm_year);
    printf("End date: ");
    scanf("%d %d %d",&end_date.tm_mday,&end_date.tm_mon,&end_date.tm_year);
    start_date.tm_hour = 0;  start_date.tm_min = 0;  start_date.tm_sec = 0;
    end_date.tm_hour = 0;  end_date.tm_min = 0;  end_date.tm_sec = 0;
    start_time = mktime(&start_date);
    end_time = mktime(&end_date);
    seconds = difftime(end_time, start_time);
    printf ("%d days difference\n", (int) (0.5 + seconds/(60*60*24)));
    return 0;
}

测试

Start date: 23 11 2017
End date: 27 11 2017
4 days difference

Answer 2

在调用mktime()之前，代码无法设置所需的字段。结果：未定义的行为。

struct tm BD;

// these 3 lines of code do nothing
BD.tm_mday;        
BD.tm_mon;         
BD.tm_year;

scanf("%d %d %d",&BD.tm_mday,&BD.tm_mon,&BD.tm_year);
// Only 3 of the 9+ fields of `BD` have a defined value.

首先将结构归零并设置tm_isdst。要正确使用mktime()，除了tm_yday和tm_wday之外，所有字段都需要先设置。这两个字段因阅读而被忽略。所有字段都更新为其主要范围。

由于struct tm可能包含超过定义的9个字段集，因此很容易将整个结构的字段初始化为零，以确保所有字段都已设置。编码器经常忘记设置tm_isdst和其他可选字段，导致结果不一致。

#include <stdio.h>
#include <time.h>

int main(void) {
  struct tm BD = { 0 };
  // Set to -1 to direct mktime() to decide if DST applies or not.
  // or set to 0, or 1, if a specific DST flag is desired.
  BD.tm_isdst = -1; 
  struct tm KT = { 0 };
  KT.tm_isdst = -1; 

  printf("Start date: ");
  if (3 != scanf("%d %d %d", &BD.tm_mday, &BD.tm_mon, &BD.tm_year)) return -1;

  printf("End date: ");
  if (3 != scanf("%d %d %d", &KT.tm_mday, &KT.tm_mon, &KT.tm_year)) return -1;

  double sec = difftime(mktime(&KT), mktime(&BD));

  printf("%f\n", sec);
  return 0;
}

计算键盘输入的2个日期之间的天数

2 个答案: