malloc和释放calloc怎么会用不同的签名？ [英] How did malloc and calloc end up with different signatures?

问题描述

可能重复：结果
  <一href=\"http://stackoverflow.com/questions/7536413/why-calloc-takes-two-arguments-while-malloc-only-one\">Why释放calloc需要两个参数，而malloc的只有一个？

有地段的说明的malloc 和释放calloc 之间的功能差异的资源，但我不能很容易地找到一个描述了不同的函数签名背后的历史：

There are lots of resources describing the difference in functionality between malloc and calloc, but I can't easily find one that describes the history behind the differing function signatures:

   void *calloc(size_t nmemb, size_t size);
   void *malloc(size_t size);

当然，尺寸前者是每个成员的大小。也许这个想法是多重的最页大小尺寸会员可以callocs懒洋洋地通过操作系统来实现？

Of course, the size in the former is the size for each member. Maybe the idea was that multiple-of-the-page-size member size callocs could be done lazily via the OS?

（我可以弥补的原因，以及未来的家伙 - 没有公认的答案，而不引用来源： - ）

(I can make up reasons as well as the next guy -- no accepted answers without cited sources. :-)

推荐答案

这是在C规范使用的语言间pretation有所开放。

This is somewhat open to interpretation of the language used in the C specification.

这里的语言似乎很认真选择 - malloc的是在第7.20.3.3的定义是：

The language here seems very carefully chosen - malloc is defined in section 7.20.3.3 as:

malloc函数为对象，其大小为分配空间
  由size指定，其值是不确定的。

The malloc function allocates space for an object whose size is specified by size and whose value is indeterminate.

此前的对象是在3.14节定义为：

Earlier an object was defined in section 3.14 as:

在执行环境中的数据存储的区域，该
  其中的内容可以重新present值

region of data storage in the execution environment, the contents of which can represent values

另一方面释放calloc在7.20.3.1所定义：

calloc on the other hand is defined in 7.20.3.1 as:

在释放calloc功能nmemb个对象的数组分配空间，
  每个其尺寸是尺寸。该空间被初始化为所有位
  零。

The calloc function allocates space for an array of nmemb objects, each of whose size is size. The space is initialized to all bits zero.

这应该很明显。释放calloc和malloc的之间的不同之处在于释放calloc对于n概念对象数组分配内存，尽管在实践中，这是从对malloc呼叫这对于尺寸为1概念性对象分配空间没有不同（正*大小）。

This should make it obvious. The difference between calloc and malloc is that calloc allocates memory for an array of n conceptual objects, although in practice this is no different from a call to malloc which allocates space for 1 conceptual object of size (n * size).

因此​​，接下来的问题是...什么是需要空间的区别为对象的数组和空间的一大对象？

So the next question is... what is the need for the distinction between space for an array of objects and space for one large object?

从程序员的角度来看这两个函数调用只是要求不同的事情。一个是要求大内存大块被分配 - 我会处理的。另一种是说 - 我想要的n个事物的数组这是这种规模的，给我一些记忆，我可以使用这个数组和零它 - 因为在大多数实现我可以做什么清零的内存意味着良好的假设

From a programmers perspective the two function calls are just asking for different things. One is asking for a big hunk of memory to be assigned - and I'll deal with it. The other is saying - I want an array of n things which are of this size, give me some memory which I could use for this array, and zero it - because in most implementations I can make good assumptions about what zeroed memory means.

这是您要使用它的malloc +调零，通过我的阅读说明书，关于该功能的目的误解的事实。

The fact that you are trying to use it as malloc + zeroing is, by my reading of the specification, a misunderstanding about the purpose of the function.

他们结束了与不同的签名，因为他们做不同的事情。

They ended up with different signatures because they do different things.

有些可爱的一面的想法...一个平凡的malloc实现可以如下：

Some cute side thoughts... A trivial malloc implementation can look like:

#define malloc(x) (calloc(1, x))

这也是有趣的注意的是，如果我的NULL指针重新presentation不归零，然后释放calloc将不会返回NULL我一个指针数组。更妙的是，如果我重新设计在清零的内存presentation整数不是（（INT）0），释放calloc将不会返回我0的数组。

It is also fun to note that if my NULL pointer representation is not zeroed, then calloc won't return me an array of NULL pointers. Better yet, if I design an integer representation in which zeroed memory is not ((int)0), calloc won't return me an array of 0s.

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