blocks|key|2980301|text|sizeof运算符生成类型的大小(以字节为单位)，其中字节被定义为char的大小。因此，根据定义，sizeof(char)始终是1，而不管char在给定平台上有多少位。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2980302|这适用于C和C%2B%2B。|2980303|来自C11标准，6.5.3.4|BOLD|2980304|blockquote|2980305|sizeof运算符生成其操作数的大小(以字节为单位)，该操作数可能是一个表达式或类型的括号大小名称。大小由操作数的类型确定.|ordered-list-item|2980306|然后,|2980307|2980308|当sizeof应用于具有char、unsigned+char或signed+char类型(或其限定版本)的操作数时，结果为1。|2980309|来自C%2B%2B11标准，5.3.3|2980310|2980311|sizeof运算符在其操作数的对象表示中生成字节数。操作数要么是一个表达式，它是一个未计算的操作数(第5条)，要么是带括号的类型-id..+sizeof(char)**，**+sizeof(signed+char)+和+sizeof(unsigned+char)+是1.|2980312|(强调地雷)|2980313|entityMap^0|0|6|X|4|1D|C|1X|4|0|0|8|7|0|0|0|6|0|0|0|1|6|C|4|H|D|V|B|0|A|5|0|0|0|6|1Y|C|2G|J|32|L|1Y|E|2G|J|30|1|32|L|3O|3|0|0^^$0|@$1|2|3|4|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]|$9|18|A|19|B|C]|$9|1A|A|1B|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1C|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1D|8|@$9|1E|A|1F|B|J]]|D|@]|E|$]]|$1|K|3|-4|5|L|7|1G|8|@]|D|@]|E|$]]|$1|M|3|N|5|O|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|1K|8|@]|D|@]|E|$]]|$1|R|3|-4|5|L|7|1L|8|@]|D|@]|E|$]]|$1|S|3|T|5|O|7|1M|8|@$9|1N|A|1O|B|C]|$9|1P|A|1Q|B|C]|$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@]|E|$]]|$1|U|3|V|5|6|7|1V|8|@$9|1W|A|1X|B|J]]|D|@]|E|$]]|$1|W|3|-4|5|L|7|1Y|8|@]|D|@]|E|$]]|$1|X|3|Y|5|O|7|1Z|8|@$9|20|A|21|B|C]|$9|22|A|23|B|C]|$9|24|A|25|B|C]|$9|26|A|27|B|C]|$9|28|A|29|B|J]|$9|2A|A|2B|B|J]|$9|2C|A|2D|B|J]|$9|2E|A|2F|B|J]|$9|2G|A|2H|B|J]]|D|@]|E|$]]|$1|Z|3|10|5|6|7|2I|8|@]|D|@]|E|$]]|$1|11|3|-4|5|6|7|2J|8|@]|D|@]|E|$]]]|12|$]]

The <code>sizeof</code> operator yields the size of a type in bytes, where a byte is defined to be the size of a <code>char</code>. So <code>sizeof(char)</code> is always 1 by definition, regardless of how many bits <code>char</code> has on a given platform.

This applies to both C and C++.

<hr>

From the C11 standard, 6.5.3.4

<blockquote>
 <ol start="2">
 <li>The <code>sizeof</code> operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand....
 </li>
 </ol>
</blockquote>

Then,

<blockquote>
 <ol start="4">
 <li>When <code>sizeof</code> is applied to an operand that has type <code>char</code>, <code>unsigned char</code>, or <code>signed char</code>, (or a qualified version thereof) the result is 1.</li>
 </ol>
</blockquote>

From the C++11 standard, 5.3.3

<blockquote>
 <ol>
 <li>The <code>sizeof</code> operator yields the number of bytes in the object representation of its operand. The operand is either an expression, which is an unevaluated operand (Clause 5), or a parenthesized type-id.... ... <code>sizeof(char)</code>, <code>sizeof(signed char)</code> and <code>sizeof(unsigned char)</code> are 1.</li>
 </ol>
</blockquote>

(emphasis mine)

blocks|key|1681840|text|sizeof(x)返回以char大小单位表示的x大小。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1681841|entityMap^0|0|9|C|4|N|1|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

<code>sizeof(x)</code> is returning the size of <code>x</code> expressed in units of size of <code>char</code>.

blocks|key|1668478|text|您只是混淆了、字节、和octets。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1668479|字节是一个字符的大小。这将生成始终为真的sizeof(char)+==+1，因为sizeof返回以字节为单位的大小。|CODE|1668480|而八进制则由8位组成。|1668481|在几乎所有的现代平台上，字节的大小与八位字节的大小是一致的。这就是为什么把它们混为一谈是一个常见的错误，就连书作者和教授也在这样做。|1668482|entityMap^0|7|3|B|6|0|K|H|14|6|1D|6|0|1|3|6|2|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|H]|$9|W|A|X|B|H]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|I|3|J|5|6|7|10|8|@$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|K|3|L|5|6|7|15|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|N|$]]

You're just confused with the difference between bytes and octets.

A byte is the size of one character. This yields to the always true <code>sizeof(char) == 1</code>, because <code>sizeof</code> return the size in bytes

While an octet consists out of 8 bits.

On almost all modern platforms, the size of a byte is coincidentally the same as of an octet. That's the reason why it's a common error to mix them up, even book authors and professors are doing this.

blocks|key|2980420|text|问题应该是--假设在一个假设的机器中，word+size(size+of+registers)是32位。多少(煤焦)还会有多少？|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2980421|答案是1+byte。|2980422|在计算中，word是特定处理器设计所使用的自然数据单位的术语。word是由指令集或处理器的硬件作为一个单元处理的固定大小的数据。字中的位数(字大小、字宽或字长)是任何特定处理器设计或计算机结构的一个重要特征。--+architecture%2529|blockquote|2980423|在这种情况下，word-size将是32位。也是|2980424|从历史上看，字节是计算机中用于编码单个文本字符的位数，因此它是许多计算机体系结构中最小的可寻址内存单元。--+https://en.wikipedia.org/wiki/Byte|2980425|1字节是最小的可寻址内存单位，它是硬件规范选择的8位、9位或16位。|2980426|就sizeof而言，它首先确定参数的类型，最后以字节为单位计算大小。因此，下面两个C%2B%2B语句将产生相同的结果。|2980427|++int+n;
++std::cout<<sizeof(int);
++std::cout<<sizeof(n);|code-block|syntax|javascript|2980428|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Word_%2528computer_architecture%2529|1|https://en.wikipedia.org/wiki/Byte^0|J|S|0|3|6|0|2Z|F|0|0|7|9|0|1J|Y|1|0|0|1|6|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|1D|8|@]|D|@$9|1E|A|1F|1|1G]]|E|$]]|$1|K|3|L|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|M|3|N|5|J|7|1K|8|@]|D|@$9|1L|A|1M|1|1N]]|E|$]]|$1|O|3|P|5|6|7|1O|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1P|8|@$9|1Q|A|1R|B|C]]|D|@]|E|$]]|$1|S|3|T|5|U|7|1S|8|@]|D|@]|E|$V|W]]|$1|X|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]]|Y|$Z|$5|10|11|12|E|$13|14]]|15|$5|10|11|12|E|$13|16]]]]

The question should have been -- Suppose in a hypothetical machine, the <code>word size(size of registers)</code> is 32 bits. What would sizeof(char) return?

And answer will be <code>1 byte</code>.

<blockquote>
 In computing, word is a term for the natural unit of data used by a
 particular processor design. A word is a fixed-sized piece of data
 handled as a unit by the instruction set or the hardware of the
 processor. The number of bits in a word (the word size, word width, or
 word length) is an important characteristic of any specific processor
 design or computer architecture. -- <a href="https://en.wikipedia.org/wiki/Word_%28computer_architecture%29" rel="nofollow">https://en.wikipedia.org/wiki/Word_%28computer_architecture%29</a>
</blockquote>

In you case <code>word-size</code> will be 32 bits. Also

<blockquote>
 Historically, the byte was the number of bits used to encode a single
 character of text in a computer and for this reason it is the smallest
 addressable unit of memory in many computer architectures. -- <a href="https://en.wikipedia.org/wiki/Byte" rel="nofollow">https://en.wikipedia.org/wiki/Byte</a>
</blockquote>

1 byte is smallest addressable unit of memory, it cat be 8 bit , 9 bits or 16 bits anything that hardware spec chooses.

As far as <code>sizeof</code> is concerned it first determines the type of argument, eventually computes the size in bytes. So, following two C++ statements will produce same result.

<pre><code> int n;
 std::cout&lt;&lt;sizeof(int);
 std::cout&lt;&lt;sizeof(n);
</code></pre>

blocks|key|3448228|text|没有大小(Char)为4的机器，它总是1字节。该字节可能包含32位，但就C编译器而言，它是一个字节。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3448229|"8位“的正确名称是八位。C标准对一个字符大小的对象使用“字节”一词。其他人可能以不同的方式使用“字节”一词，通常是指“八进制”，但在C(和C%2B%2B，或object)中，它的意思是“字符大小的对象”。一个字符可能超过8位，或者超过一个八进制，但它总是一个字节。|3448230|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

There are no machines where sizeof(char) is 4. It's always 1 byte. That byte might contain 32 bits, but as far as the C compiler is concerned, it's one byte.

The correct name for "8 bits" is octet. The C Standard uses the word "byte" for an object that is the size of a char. Others may use the word "byte" in different ways, often when they mean "octet", but in C (and C++, or Objective-C) it means "object the size of a char". A char may be more than 8 bits, or more than one octet, but it's always one byte.

I was learning C++ and come across the following question. I'm just a beginner and I got confused. Isn't sizeof() function supposed to return the size of the datatype? Why could a data object has different size from its sizeof()? I don't understand the explanation of the answer. 

Suppose in a hypothetical machine, the size of char is 32 bits. What would sizeof(char) return?

a) 4

b) 1

c) Implementation dependent

d) Machine dependent

Answer:b

Explanation: The standard does NOT require a char to be 8-bits, but does require that sizeof(char) return 1.

The difference between size of datatype and sizeof(data type)

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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我当时正在学习C++，并遇到了以下问题。我只是个初学者我很困惑。函数不是应该返回数据类型的大小吗？为什么数据对象的大小可以与其size Why ()不同？我不明白答案的解释。假设在一台假设的机器中，字符的大小是32位。多少(煤焦)还会有多少？( a) 4( b) 1c)取决于执行情况d)依赖于机器答:B说明:标准不要求...

问数据类型大小与大小之间的差异(数据类型)
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