Question

我想在格式struct“tm”中添加延迟，所以我运行此代码：

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

#define SEC_PER_DAY 86400

#define SEC_PER_HR 3600

#define SEC_PER_MIN 60

int main(void) {
    time_t     now;
    time_t     time_delay;
    struct tm *ts;
    struct tm *ts_delay;
    char       buf[140];
    char       buf_delay[140];
    now = time(NULL);
    int delay =100;

    ts_delay = localtime(&now);

    printf("day = %d \n",ts_delay->tm_mday);
    ts_delay->tm_mday += delay /SEC_PER_DAY;
    printf("day = %d \n",ts_delay->tm_mday);
    printf("hour = %d \n",ts_delay->tm_hour);
    ts_delay->tm_hour += (delay%SEC_PER_DAY)/SEC_PER_HR;
    printf("hour = %d \n",ts_delay->tm_hour);
    printf("min = %d \n",ts_delay->tm_min);
    ts_delay->tm_min += ((delay%SEC_PER_DAY)%SEC_PER_HR)/SEC_PER_MIN;
    printf("min = %d \n",ts_delay->tm_min);
    printf("sec = %d \n",ts_delay->tm_sec);
    ts_delay->tm_sec += ((delay%SEC_PER_DAY)%SEC_PER_HR)%SEC_PER_MIN;
    printf("sec = %d \n",ts_delay->tm_sec);

    /* Format and print the time, "ddd yyyy-mm-dd hh:mm:ss zzz" */
    ts = localtime(&now);


    strftime(buf, sizeof(buf), "%FT%T%z", ts);
    strftime(buf_delay, sizeof(buf_delay), "%FT%T%z", ts_delay);
    puts(buf);
    puts(buf_delay);
    return 0; 
}

结果：

day = 6
day = 6
hour = 4
hour = 4
min = 14
min = 15
sec = 24
sec = 64
2013-12-06T04:14:24-0600 ==> ts
2013-12-06T04:14:24-0600 ==> ts_delay

似乎延迟没有添加到ts_delay !!

任何向正确方向的推动都会非常有用thx

Answer 1

您的struct tm * ts_delay被localtime()的号码覆盖你有这个代码：

ts_delay = localtime(&now);
... change ts_delay;
ts = localtime(&now);

现在，localtime()返回一个指针。因此必须分配一些存储，以便localtime的返回值可以指向somwhere有效。运行时将在单个静态缓冲区（可能是每个线程）中为该结果分配该存储 of localtime（）。因此2.调用localtime（）将覆盖ts_delay指向的相同缓冲区。

而是将localtime（）的结果复制到您自己管理的存储中，而不是将struct tm指针用于单个可用缓冲区。

struct tm ts;      //not a pointer anymore
struct tm ts_delay;

ts_delay = *localtime(&now); //copy the returned struct
... change ts_delay;
ts = *localtime(&now);

如果您的平台提供，请使用getlocaltime_r，例如

localtime_r(&now, &ts);

为时间格式struct“tm”添加延迟

1 个答案: