Linux 将毫秒转换为 GNU 端口的时间规范

Convert milliseconds to timespec for GNU port

提问by jparthj

I want to convert milliseconds into timespec structure used by GNU Linux. I have tried following code for the same.

我想将毫秒转换为 GNU Linux 使用的 timespec 结构。我已经尝试过以下代码。

  timespec GetTimeSpecValue(unsigned long milisec)
  {
    struct timespec req;
    //long sec = (milisecondtime /1000);
    time_t sec = (time_t)(milisec/1000);
    req->tv_sec = sec;
    req->tv_nsec = 0;
    return req;
  }

Running this code gives me the following error.

运行此代码给我以下错误。

expected ‘=', ‘,', ‘;', ‘asm' or ‘__attribute__' before ‘GetTimeSpecValue'

'GetTimeSpecValue' 之前的预期 '=', ',', ';', 'asm' 或 '__attribute__'

I have also include time.hfile in the code.

我还在代码中包含time.h文件。

采纳答案by hetepeperfan

The timespecstructure represents time in two portions — seconds and nanoseconds. Thus, the algorithm for conversion from milliseconds is pretty darn simple. One seconds has thousand milliseconds, one milliseconds has a thousand microseconds and one microsecond has a thousand nanoseconds, for which we are grateful to SI. Therefore, we first need to divide milliseconds by a thousand to get a number of seconds. Say, for example, 1500 milliseconds / 1000 = 1.5 seconds. Given integer arithmetics (not a floating point), the remainder is dropped (i.e. 1500 / 1000 is equal to just 1, not 1.5). Then we need to take a remainder that denotes a number of milliseconds that is definitely less than one second, and multiply it by a million to convert it to nanoseconds. To get a remainder of dividing by 1000, we use a module operator (%)(i.e. 1500 % 1000 is equal to 500). For example, let's convert 4321 milliseconds to seconds and nanoseconds:

该timespec结构以两部分表示时间——秒和纳秒。因此，从毫秒转换的算法非常简单。一秒有一千毫秒，一毫秒有一千微秒，一微秒有一千纳秒，为此我们感谢SI。因此，我们首先需要将毫秒除以一千来得到秒数。比如说，1500 毫秒 / 1000 = 1.5 秒。给定整数算术（不是浮点数），余数被丢弃（即 1500 / 1000 等于 1，而不是 1.5）。然后我们需要取一个表示绝对小于一秒的毫秒数的余数，并将其乘以一百万以将其转换为纳秒。要得到除以 1000 的余数，我们使用模块运算符 ( %)（即1500 % 1000 is equal to 500）。例如，让我们将 4321 毫秒转换为秒和纳秒：

1. 4321 (milliseconds) / 1000 = 4 (seconds)
2. 4321 (milliseconds) % 1000 = 321 (milliseconds)
3. 321 (milliseconds) * 1000000 = 321000000 (nanoseconds)

1. 4321（毫秒）/ 1000 = 4（秒）
2. 4321（毫秒）% 1000 = 321（毫秒）
3. 321（毫秒）* 1000000 = 321000000（纳秒）

Knowing the above, the only thing that is left is to write a little bit of C code. There are few things that you didn't get right:

知道了上面的内容，剩下的就是写一点C代码了。有几件事你没有做对：

1. In C, you have to prefix structure data types with struct. For example, instead of saying timespecyou say struct timespec. In C++, however, you don't have to do it (unfortunately, in my opinion).
2. You cannot return structures from the function in C. Therefore, you need to pass a structure by pointer into a function that does something with that structure.

1. 在 C 中，您必须在结构数据类型前加上struct. 例如，与其说timespec你说struct timespec。但是，在 C++ 中，您不必这样做（不幸的是，在我看来）。
2. 您不能从 C 中的函数返回结构。因此，您需要通过指针将结构传递给对该结构执行某些操作的函数。

Edit: This contradicts (Return a `struct` from a function in C).

编辑：这与（从 C 中的函数返回一个 `struct`相矛盾）。

OK, enough talking. Below is a simple C code example:

好了，聊够了。下面是一个简单的 C 代码示例：

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

static void ms2ts(struct timespec *ts, unsigned long ms)
{
    ts->tv_sec = ms / 1000;
    ts->tv_nsec = (ms % 1000) * 1000000;
}

static void print_ts(unsigned long ms)
{
    struct timespec ts;
    ms2ts(&ts, ms);
    printf("%lu milliseconds is %ld seconds and %ld nanoseconds.\n",
           ms, ts.tv_sec, ts.tv_nsec);
}

int main()
{
    print_ts(1000);
    print_ts(2500);
    print_ts(4321);
    return EXIT_SUCCESS;
}

Hope it helps. Good Luck!

希望能帮助到你。祝你好运！

回答by hetepeperfan

try this:

尝试这个：

struct timespec GetTimeSpecValue(unsigned long millisec) {
    struct timespec req;
    req.tv_sec=  (time_t)(millisec/1000);
    req.tv_nsec = (millisec % 1000) * 1000000;
    return req;
}

I don't think struct timespec is typedef'ed,hence you need to prepend timespec with struct. And work out the nano second part if you want to be precise. Note that req is not a pointer. Thus members cannot be accessed with '->'

我不认为 struct timespec 是 typedef'ed，因此您需要在 timespec 前面加上 struct。如果你想精确的话，计算出纳秒部分。请注意， req 不是指针。因此不能使用“->”访问成员

回答by trench_digger

Incorporating a few tweaks to the answer including Geoffrey's comment, the code below avoids divides for small delay and modulo for long delay:

对答案进行了一些调整，包括 Geoffrey 的评论，下面的代码避免了小延迟的除法和长延迟的取模：

void msec_to_timespec(unsigned long msec, struct timespec *ts)
{
    if (msec < 1000){
        ts->tv_sec = 0;
        ts->tv_nsec = msec * 1000000;
    }
    else {
        ts->tv_sec = msec / 1000;
        ts->tv_nsec = (msec - ts->tv_sec * 1000) * 1000000;
    }
}