blocks|key|4224520|text|对time(NULL)的调用返回当前日历时间(自1970年1月1日以来的秒数)。详情请参见this+reference。通常，如果您传入一个指向time_t指针的指针，该指针变量将指向当前时间。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4224521|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/clibrary/ctime/time/^0|1|A|20|6|19|E|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]]|E|$]]|$1|F|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

The call to <code>time(NULL)</code> returns the current calendar time (seconds since Jan 1, 1970). See <a href="http://www.cplusplus.com/reference/clibrary/ctime/time/" rel="noreferrer">this reference</a> for details. Ordinarily, if you pass in a pointer to a <code>time_t</code> <a href="http://www.cplusplus.com/reference/clibrary/ctime/time_t/" rel="noreferrer">variable</a>, that pointer variable will point to the current time.

blocks|key|4224544|text|您可以传入一个指向time_t对象的指针，time将用当前时间填充该对象(返回值与您所指向的值相同)。如果传入NULL，它就会忽略它，只返回一个表示当前时间的新time_t对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4224545|entityMap^0|9|6|L|4|1J|4|28|6|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

You can pass in a pointer to a <code>time_t</code> object that <code>time</code> will fill up with the current time (and the return value is the same one that you pointed to). If you pass in <code>NULL</code>, it just ignores it and merely returns a new <code>time_t</code> object that represents the current time.

blocks|key|4224562|text|time函数返回自某个时间点(在Unix系统上，自1970年1月1日午夜以来)以秒为单位的当前时间(以time_t值的形式)，它接受一个参数，即存储时间的time_t指针。将NULL作为参数传递会导致time将时间作为正常返回值返回，但不会将其存储在其他任何地方。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4224563|entityMap^0|0|4|1F|6|25|6|2F|4|2S|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]|$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|G|$]]

The <code>time</code> function returns the current time (as a <code>time_t</code> value) in seconds since some point (on Unix systems, since midnight UTC January 1, 1970), and it takes one argument, a <code>time_t</code> pointer in which the time is stored. Passing <code>NULL</code> as the argument causes <code>time</code> to return the time as a normal return value but not store it anywhere else.

blocks|key|535071|text|您必须参考documentation+for+ctime。time是一个函数，它接受类型为time_t+*+(指向time_t对象的指针)的一个参数，并将当前时间赋给它。除了传递这个指针，您还可以传递NULL，然后使用返回的time_t值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|535072|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cplusplus.com/reference/clibrary/ctime/time/^0|T|4|19|8|1L|6|2S|4|5|N|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]|$9|Q|A|R|B|C]|$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@$9|W|A|X|1|Y]]|E|$]]|$1|F|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

You have to refer to the <a href="http://www.cplusplus.com/reference/clibrary/ctime/time/" rel="nofollow">documentation for ctime</a>. <code>time</code> is a function that takes one parameter of type <code>time_t *</code> (a pointer to a <code>time_t</code> object) and assigns to it the current time. Instead of passing this pointer, you can also pass <code>NULL</code> and then use the returned time_t value instead.

blocks|key|537784|text|Time：它返回自1970年1月1日纪元以来所经过的时间|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|537785|entityMap^0|0|4|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

<code>Time</code> : It returns the time elapsed in seconds since the epoch 1 Jan 1970

blocks|key|4508812|text|您可以传入一个指向time_t对象的指针，该对象的时间将由当前时间填充(返回值与您所指向的值相同)。如果传入NULL，它就会忽略它，只返回一个表示当前时间的新time_t对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4508813|Nb:time(&timer);等同于timer+=+time(NULL);|4508814|entityMap^0|9|6|1I|4|27|6|0|0|G|J|J|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|I|$]]

You can pass in a pointer to a <code>time_t</code> object that time will fill up with the current time (and the return value is the same one that you pointed to). If you pass in <code>NULL</code>, it just ignores it and merely returns a new <code>time_t</code> object that represents the current time.

<code>Nb:time(&amp;timer);</code> is equivalent to <code>timer = time(NULL);</code>

blocks|key|537832|text|int+main+(void)
{+++
++++//print+time+in+seconds+from+1+Jan+1970+using+c+++
++++float+n+=+time(NULL);+++
++++printf("%25.2f\n"+,+n);++++++
}++++++|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|537833|这将打印1481986944.00+(此时)。|unstyled|537834|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>int main (void)
{ 
 //print time in seconds from 1 Jan 1970 using c 
 float n = time(NULL); 
 printf("%.2f\n" , n); 
} 
</code></pre>

this prints 1481986944.00 (at this moment).

blocks|key|4224816|text|[从duplicate,+now-deleted+question复制的答案。]|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4224817|time()是一个非常非常老的函数。它可以追溯到C语言甚至还没有long类型的时代。曾几何时，获得32位类型的唯一方法是使用一个由两个int组成的数组--当时int是16位的。|style|CODE|4224818|所以你打电话给|4224819|int+now[2];
time(now);|code-block|syntax|javascript|4224820|它将32位时间填充到now[0]和now[1]中，一次16位。(这就解释了为什么其他与时间相关的函数，如localtime和ctime，也倾向于通过指针接受它们的时间参数。)|4224821|后来，dmr完成了将long添加到编译器的工作，因此您可以开始说|4224822|long+now;
time(&now);|4224823|后来，有人意识到，如果time()继续返回值，而不是仅仅通过指针填充它，那么它会很有用。但是-向后兼容性是一件很棒的事情-为了所有仍在执行指针的代码的好处，time()函数必须继续支持time(&now)参数。这就是为什么--这也是为什么向后兼容性并不总是那么美妙的原因，毕竟--如果你使用返回值，你仍然需要传递NULL作为指针：|4224824|long+now+=+time(NULL);|4224825|(当然，更晚些时候，我们开始多次使用time_t而不是普通的long，例如，可以将其更改为64位类型，从而避开y2.038k+problem。)|4224826|[附注:我实际上不确定从int+[2]到long的更改以及添加返回值的更改是在不同的时间发生的；它们可能是同时发生的。但请注意，当时间表示为数组时，它必须通过指针填充，它不能作为值返回，因为C函数当然不能返回数组。]|4224827|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/46002228|1|https://en.wikipedia.org/wiki/Dennis_Ritchie|2|https://en.wikipedia.org/wiki/Year_2038_problem^0|2|V|0|0|0|6|W|4|1V|3|27|3|0|0|0|A|6|H|6|1G|9|1Q|5|0|A|4|3|3|1|0|0|B|6|26|6|2K|A|0|0|I|6|U|4|1J|F|2|0|C|7|K|4|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@$A|1F|B|1G|1|1H]]|C|$]]|$1|D|3|E|5|6|7|1I|8|@$A|1J|B|1K|F|G]|$A|1L|B|1M|F|G]|$A|1N|B|1O|F|G]|$A|1P|B|1Q|F|G]]|9|@]|C|$]]|$1|H|3|I|5|6|7|1R|8|@]|9|@]|C|$]]|$1|J|3|K|5|L|7|1S|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1T|8|@$A|1U|B|1V|F|G]|$A|1W|B|1X|F|G]|$A|1Y|B|1Z|F|G]|$A|20|B|21|F|G]]|9|@]|C|$]]|$1|Q|3|R|5|6|7|22|8|@$A|23|B|24|F|G]]|9|@$A|25|B|26|1|27]]|C|$]]|$1|S|3|T|5|L|7|28|8|@]|9|@]|C|$M|N]]|$1|U|3|V|5|6|7|29|8|@$A|2A|B|2B|F|G]|$A|2C|B|2D|F|G]|$A|2E|B|2F|F|G]]|9|@]|C|$]]|$1|W|3|X|5|L|7|2G|8|@]|9|@]|C|$M|N]]|$1|Y|3|Z|5|6|7|2H|8|@$A|2I|B|2J|F|G]|$A|2K|B|2L|F|G]]|9|@$A|2M|B|2N|1|2O]]|C|$]]|$1|10|3|11|5|6|7|2P|8|@$A|2Q|B|2R|F|G]|$A|2S|B|2T|F|G]]|9|@]|C|$]]|$1|12|3|-4|5|6|7|2U|8|@]|9|@]|C|$]]]|13|$14|$5|15|16|17|C|$18|19]]|1A|$5|15|16|17|C|$18|1B]]|1C|$5|15|16|17|C|$18|1D]]]]

[Answer copied from a <a href="https://stackoverflow.com/questions/46002228">duplicate, now-deleted question</a>.]
<code>time()</code> is a very, very old function. It goes back to a day when the C language didn't even have type <code>long</code>. Once upon a time, the only way to get something like a 32-bit type was to use an array of two <code>int</code>s — and that was when <code>int</code>s were 16 bits.
So you called
<pre><code>int now[2];
time(now);
</code></pre>
and it filled the 32-bit time into <code>now[0]</code> and <code>now[1]</code>, 16 bits at a time. (This explains why the other time-related functions, such as <code>localtime</code> and <code>ctime</code>, tend to accept their time arguments via pointers, too.)
Later on, <a href="https://en.wikipedia.org/wiki/Dennis_Ritchie" rel="nofollow noreferrer">dmr</a> finished adding <code>long</code> to the compiler, so you could start saying
<pre><code>long now;
time(&amp;now);
</code></pre>
Later still, someone realized it'd be useful if <code>time()</code> went ahead and returned the value, rather than just filling it in via a pointer. But — backwards compatibility is a wonderful thing — for the benefit of all the code that was still doing <code>time(&amp;now)</code>, the <code>time()</code> function had to keep supporting the pointer argument. Which is why — and this is why backwards compatibility is not always such a wonderful thing, after all — if you're using the return value, you still have to pass NULL as a pointer:
<pre><code>long now = time(NULL);
</code></pre>
(Later still, of course, we started using <code>time_t</code> instead of plain <code>long</code> for times, so that, for example, it can be changed to a 64-bit type, dodging the <a href="https://en.wikipedia.org/wiki/Year_2038_problem" rel="nofollow noreferrer">y2.038k problem</a>.)
[P.S. I'm not actually sure the change from <code>int [2]</code> to <code>long</code>, and the change to add the return value, happened at different times; they might have happened at the same time. But note that when the time was represented as an array, it had to be filled in via a pointer, it couldn't be returned as a value, because of course C functions can't return arrays.]

I learning about some basic C functions and have encountered <code>time(NULL)</code> in some manuals.

What exactly does this mean?

What is time(NULL) in C?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我学习了一些基本的C函数，并在一些手册中遇到过time(NULL)。这到底是什么意思？

问在C中时间(NULL)是什么？
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问在C中时间(NULL)是什么？EN