前提：本例中规定日期的格式为YYYY-MM-DD

1、判断单个日期是否合法

int check_date(int year, int month, int day)
{
        int monthDays[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

        if ( year < 0 )
        {
                printf("the entered year[%d] is invalid\n", year);
                return -1;
        }

        if ( month < 1 || month > 12 )
        {
                printf("The entered month[%d] is invalid\n", month);
                return -1;
        }

        if ( month == 2 )
        {
                // 判断如果是闰年,则修改二月的monthDays[1]值为29
                if ( (year % 400 == 0) || \
                     (year % 100 != 0 && year % 4 == 0)
                   )
                {
                        monthDays[1] = 29;
                }
        }

        if ( day < 1 || day > monthDays[month-1] )
        {
                printf("The entered day[%d] is invalid\n", day);
                return -1;
        }

        return 0;
}

2、解析输入日期字符串YYYY-MM-DD，并判断日期范围是否合法

int is_valid_date(const char *startDate, const char *endDate)
{
        int start_year = 0;
        int start_month = 0;
        int start_day = 0;
        int end_year = 0;
        int end_month = 0;
        int end_day = 0;

        if ( strlen(startDate) > 0 )
        {
                int count = 0;
                printf("\n check start date... \n");
                count = sscanf(startDate, "%4d-%2d-%2d", &start_year, &start_month, &start_day);
                if ( count != 3 )
                {
                        printf("Input parameters invalid.\n");
                        return -1;
                }

                if ( 0 != check_date(start_year, start_month, start_day) )
                {
                        return -1;
                }

                printf("\n check start date OK!\n");
        }

        if ( strlen(endDate) > 0 )
        {
                int count = 0;
                printf("\n check end date... \n");

                count = sscanf(endDate, "%4d-%2d-%2d", &end_year, &end_month, &end_day);
                if ( count != 3 )
                {
                        printf("Input parameters invalid.\n");
                        return -1;
                }

                if ( 0 != check_date(end_year, end_month, end_day) )
                {
                        return -1;
                }
                printf("\n check end date OK!\n");
        }

        printf("\n check date range...\n");
        if ( strlen(startDate) > 0 && strlen(endDate) > 0 )
        {
                if ( (end_year < start_year) || \
                     (end_year == start_year && end_month < start_month) || \
                     (end_year == start_year && end_month == start_month && end_day < start_day)
                   )
                {
                        printf("The end date is earlier than the start date!\n");
                        return -1;
                }
        }
        printf("\n check date range OK!\n");

        return 0;
}

3、测试代码

#include <stdio.h>
#include <string.h>

…… // is_valid_date()函数实现

int main(int argc, char **argv)
{
        if ( argc != 3)
        {
                printf("Usage: %s <start-date> <end-date>\n", argv[0]);
                return 0;
        }

        if ( 0 != is_valid_date(argv[1], argv[2]) )
        {
                printf("\n Input date is invalid!\n\n");
                return -1;
        }
        printf("\n start-date[%s], end-date[%s] are valid!\n\n", argv[1], argv[2]);

        return 0;
}

4、编译及测试

# gcc check_date.c -o check_date
#
#
#  ./check_date 2022-2-3 2022-4-5

 check start date...

 check start date OK!

 check end date...

 check end date OK!

 check date range...

 check date range OK!

 start-date[2022-2-3], end-date[2022-4-5] are valid!

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