blocks|key|739541|text|编辑：谢谢您的评论--我在C99标准中查找了它，在6.5.3.4节中有这样的内容：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|739542|结果的值是实现定义的，其类型(无符号整数类型)是size_t，在<stddef.h>+(和其他标头)中定义。|blockquote|CODE|739543|因此，没有指定size_t的大小，只是它必须是一个无符号整数类型。然而，在标准的第7.18.3章中可以找到一个有趣的规范：|739544|size_t极限
SIZE_MAX+65535|739545|这基本上意味着，不管size_t的大小如何，允许的值范围是0-65535，其余的是依赖于实现的。|739546|entityMap|0|LINK|mutability|MUTABLE|url|http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf^0|0|3|D|5|0|0|F|7|O|6|W|A|0|7|6|0|0|6|9|E|0|A|6|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]]|E|$]]|$1|F|3|G|5|H|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|I]|$9|18|A|19|B|I]]|D|@]|E|$]]|$1|J|3|K|5|6|7|1A|8|@$9|1B|A|1C|B|I]]|D|@]|E|$]]|$1|L|3|M|5|H|7|1D|8|@$9|1E|A|1F|B|I]|$9|1G|A|1H|B|I]]|D|@]|E|$]]|$1|N|3|O|5|6|7|1I|8|@$9|1J|A|1K|B|I]]|D|@]|E|$]]|$1|P|3|-4|5|6|7|1L|8|@]|D|@]|E|$]]]|Q|$R|$5|S|T|U|E|$V|W]]]]

EDIT: Thanks for the comments - I looked it up in the <a href="http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf" rel="nofollow noreferrer">C99 standard</a>, which says in section 6.5.3.4:

<blockquote>
 The value of the result is
 implementation-defined, and its type
 (an unsigned integer type) is <code>size_t</code>,
 defined in <code>&lt;stddef.h&gt;</code> (and other
 headers)
</blockquote>

So, the size of <code>size_t</code> is not specified, only that it has to be an unsigned integer type. However, an interesting specification can be found in chapter 7.18.3 of the standard:

<blockquote>
 limit of <code>size_t</code>
 
 <code>SIZE_MAX 65535</code>
</blockquote>

Which basically means that, irrespective of the size of <code>size_t</code>, the allowed value range is from 0-65535, the rest is implementation dependent.

blocks|key|900982|text|它应该随体系结构而变化，因为它表示任何对象的大小。因此，在32位系统上，size_t可能至少有32位宽.在64位系统上，它可能至少有64位宽。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|900983|entityMap^0|10|6|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|$]]

it should vary with the architecture because it represents the size of any object. So on a 32-bit system <code>size_t</code> will likely be at least 32-bits wide. On a 64-bit system it will likely be at least 64-bit wide.

blocks|key|901010|text|size_t在64位机上通常是64位|type|unstyled|depth|inlineStyleRanges|entityRanges|data|901011|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|$]]

size_t is 64 bit normally on 64 bit machine

blocks|key|2265140|text|size_t由C标准定义为sizeof运算符的无符号整数返回类型(C99+6.3.5.4.4)，以及malloc和C99的参数(C99+7.20.3.3等)。实际范围设置为最大值(SIZE_MAX)至少为65535+(C99+7.18.3.2)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2265141|然而，这并不让我们确定大小(Size_t)。实现可以为size_t使用它喜欢的任何表示形式，因此在大小上没有上限，而且实现也可以自由地将字节定义为16位，在这种情况下，size_t可以等效为无符号字符。|2265142|然而，抛开这一点，通常32位程序上有32位size_t，64位程序上有64位，不管数据模型如何。通常，数据模型只影响静态数据；例如，在GCC中：|2265143|`-mcmodel=small'
+++++Generate+code+for+the+small+code+model:+the+program+and+its
+++++symbols+must+be+linked+in+the+lower+2+GB+of+the+address+space.
+++++Pointers+are+64+bits.++Programs+can+be+statically+or+dynamically
+++++linked.++This+is+the+default+code+model.

`-mcmodel=kernel'
+++++Generate+code+for+the+kernel+code+model.++The+kernel+runs+in+the
+++++negative+2+GB+of+the+address+space.++This+model+has+to+be+used+for
+++++Linux+kernel+code.

`-mcmodel=medium'
+++++Generate+code+for+the+medium+model:+The+program+is+linked+in+the
+++++lower+2+GB+of+the+address+space+but+symbols+can+be+located
+++++anywhere+in+the+address+space.++Programs+can+be+statically+or
+++++dynamically+linked,+but+building+of+shared+libraries+are+not
+++++supported+with+the+medium+model.

`-mcmodel=large'
+++++Generate+code+for+the+large+model:+This+model+makes+no+assumptions
+++++about+addresses+and+sizes+of+sections.|code-block|syntax|javascript|2265144|您将注意到，指针在任何情况下都是64位的；毕竟，有64位指针而不是64位大小没有什么意义。|2265145|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|R|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

size_t is defined by the C standard to be the unsigned integer return type of the sizeof operator (C99 6.3.5.4.4), and the argument of malloc and friends (C99 7.20.3.3 etc). The actual range is set such that the maximum (SIZE_MAX) is at least 65535 (C99 7.18.3.2).

However, this doesn't let us determine sizeof(size_t). The implementation is free to use any representation it likes for size_t - so there is no upper bound on size - and the implementation is also free to define a byte as 16-bits, in which case size_t can be equivalent to unsigned char.

Putting that aside, however, in general you'll have 32-bit size_t on 32-bit programs, and 64-bit on 64-bit programs, regardless of the data model. Generally the data model only affects static data; for example, in GCC:

<pre><code>`-mcmodel=small'
 Generate code for the small code model: the program and its
 symbols must be linked in the lower 2 GB of the address space.
 Pointers are 64 bits. Programs can be statically or dynamically
 linked. This is the default code model.

`-mcmodel=kernel'
 Generate code for the kernel code model. The kernel runs in the
 negative 2 GB of the address space. This model has to be used for
 Linux kernel code.

`-mcmodel=medium'
 Generate code for the medium model: The program is linked in the
 lower 2 GB of the address space but symbols can be located
 anywhere in the address space. Programs can be statically or
 dynamically linked, but building of shared libraries are not
 supported with the medium model.

`-mcmodel=large'
 Generate code for the large model: This model makes no assumptions
 about addresses and sizes of sections.
</code></pre>

You'll note that pointers are 64-bit in all cases; and there's little point to having 64-bit pointers but not 64-bit sizes, after all.

On a 64-bit system, <code>sizeof(unsigned long)</code> depends on the data model implemented by the system, for example, it is 4 bytes on LLP64 (Windows), 8 bytes on LP64 (Linux, etc.). What's <code>sizeof(size_t)</code> supposed to be? Does it vary with data model like <code>sizeof(long)</code> does? If so, how?

<hr>

References:

<a href="http://en.wikipedia.org/wiki/64-bit#64-bit_data_models" rel="noreferrer" title="64-bit computing, 64-bit data models. On Wikipedia.">64-bit data models on Wikipedia</a>

What's sizeof(size_t) on 32-bit vs the various 64-bit data models?

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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在64位系统上，sizeof(unsigned long)依赖于系统实现的数据模型，例如，LLP64上为4个字节，LP64上为8个字节(Linux等)。sizeof(size_t)应该是什么？它是否像sizeof(long)那样随着数据模型的变化而变化？如果是这样的话，是怎么做的？参考文献：

问32位和各种64位数据模型的size_t是什么？
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问32位和各种64位数据模型的size_t是什么？EN