blocks|key|3014009|text|可能是因为我不经常需要memset和memcpy，但我不知道我会不会用过memcpy。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3014010|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Probably because it's not needed very often - I memset and memcpy reasonably often, but I don't know that I'd ever have used memswap if it was available.

blocks|key|3014063|text|我想是因为它不是经常需要的。但是，在C%2B%2B中有一种简单的方法可以做到这一点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3014064|#include+<algorithm>

swap_ranges(ptr1,+ptr1+%2B+nbytes,+ptr2)|code-block|syntax|javascript|3014065|它可能不像内置的编译器那样优化，但它有可能比你自己编写的循环更快，因为它可能有你不会实现的特定于平台的优化。|3014066|您需要小心使用上面的代码，因为它假设ptr1和ptr2是字符指针。更规范的方法是：|3014067|#include+<algorithm>

swap_ranges(ptr1,+ptr1+%2B+num_items,+ptr2)|3014068|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I think because it's not needed very often. However, there is an easy way to do this in C++:

<pre><code>#include &lt;algorithm&gt;

swap_ranges(ptr1, ptr1 + nbytes, ptr2)
</code></pre>

It's it may not be quite as optimized as a compiler built in, but it has the potential of being faster than a loop you write for yourself, since it may have platform specific optimization that you would not implement.

You do need to be careful with the above, because it assumes that ptr1 and ptr2 are char pointers. The more canonical way to do this is:

<pre><code>#include &lt;algorithm&gt;

swap_ranges(ptr1, ptr1 + num_items, ptr2)
</code></pre>

blocks|key|3014116|text|在C编程中可能不经常需要它，在C%2B%2B中，交换是对类成员做的常规事情，有std::swap算法，它针对不同的类型进行了高度优化。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3014117|entityMap|0|LINK|mutability|MUTABLE|url|http://www.sgi.com/tech/stl/swap.html^0|Z|9|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@$A|M|B|N|1|O]]|C|$]]|$1|D|3|-4|5|6|7|P|8|@]|9|@]|C|$]]]|E|$F|$5|G|H|I|C|$J|K]]]]

It probably isn't required very often in C programming, in C++ where swap is a regular thing to do on class members there's the <a href="http://www.sgi.com/tech/stl/swap.html" rel="nofollow noreferrer">std::swap</a> algorithm which is highly optimized for different types.

blocks|key|3858968|text|这不是例行公事需要的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3858969|这些想法可能已经被考虑和丢弃了，因为很难提出一个通用的算法。别忘了，C语言是一门古老的语言，扩展必须是通用的。|3858970|可能的错误条件:-|3858971|当要交换的范围重叠时的空指针行为|3858972|length+of+zero|unordered-list-item|3858973|
|3858974|running+of+memory+(最佳实现可能会为此分配内存)|3858975|3858976|null指针|3858977|3858978|最佳算法也可能取决于您正在做什么，因此可以由您直接编写更好的代码。|offset|length|style|BOLD|3858979|使用temp结构和assignment|3858980|small+length可能更快地使用|3858981|交换结构-可能更好地分配临时内存|3858982|long+length-‘|3858983|’|3858984|+section+swap+(其中section是一些最佳长度)|3858985|use+of+hardware+copy+|3858986|3858987|3858988|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|2|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1H|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|1I|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|1J|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|1K|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|1L|8|@]|9|@]|A|$]]|$1|M|3|N|5|J|7|1M|8|@]|9|@]|A|$]]|$1|O|3|L|5|6|7|1N|8|@]|9|@]|A|$]]|$1|P|3|Q|5|J|7|1O|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1Q|8|@$U|1R|V|1S|W|X]]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1T|8|@]|9|@]|A|$]]|$1|10|3|11|5|J|7|1U|8|@]|9|@]|A|$]]|$1|12|3|13|5|J|7|1V|8|@]|9|@]|A|$]]|$1|14|3|15|5|J|7|1W|8|@]|9|@]|A|$]]|$1|16|3|17|5|J|7|1X|8|@]|9|@]|A|$]]|$1|18|3|19|5|J|7|1Y|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|J|7|1Z|8|@]|9|@]|A|$]]|$1|1C|3|-4|5|6|7|20|8|@]|9|@]|A|$]]|$1|1D|3|-4|5|6|7|21|8|@]|9|@]|A|$]]|$1|1E|3|-4|5|6|7|22|8|@]|9|@]|A|$]]]|1F|$]]

This isn't something that is routinely required.

The ideas may have been considered and discarded because it is quite difficult to come up with an algorithm that is general purpose. Don't forget that C is an old language and extensions need to be generally useful.

Possible error conditions :-

<ul>
<li>behaviour when the ranges being swapped overlap</li>
<li>length of zero</li>
<li>running out of memory (an optimal implementation might allocate memory to do this)</li>
<li>null pointer</li>
</ul>

The best algorithm might also depend upon what you are doing, and so could be better coded directly by you.

<ul>
<li>swapping structures likely to be quicker using a temp structure and assignment</li>
<li>small lengths - may be better allocating temporary memory</li>
<li>long lengths - 'section' by section swap (where section is some optimal length)</li>
<li>use of hardware copy functions</li>
</ul>

Why doesn't have the c standard a memswap function, which would probably look like:

<pre><code>int memswap(void *ptr1, void *ptr2, size_t nbytes)?
</code></pre>

I know it'd be easy to write, but i think the libc could do some awesome tricks to speed it up like some implementations do it for memcpy.

Why isn't there a standard memswap function

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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为什么没有c标准的内存交换函数，它可能看起来像这样：int memswap(void *ptr1, void *ptr2, size_t nbytes)?我知道这很容易写，但我认为libc可以做一些很棒的技巧来加速它，就像一些实现为memcpy所做的那样。

问为什么没有一个标准的memswap函数
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问为什么没有一个标准的memswap函数EN