blocks|key|1277642|text|空结构，如isbadawi+mentions。此外，gcc还允许arrays+of+0+size|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1277643|int+a[0];
sizeof(a);|code-block|syntax|javascript|1277644|编辑:在看到MSDN链接后，我尝试了VS2005中的空结构，sizeof返回了1。我不确定这是不是VS的错误，或者规范在某种程度上是灵活的|1277645|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/users/281108/isbadawi|1|https://stackoverflow.com/questions/2632021/can-sizeof-return-0-zero/2632031#2632031|2|http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html^0|5|8|0|E|8|1|W|G|2|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]|$A|10|B|11|1|12]|$A|13|B|14|1|15]]|C|$]]|$1|D|3|E|5|F|7|16|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|17|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|18|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]|S|$5|N|O|P|C|$Q|T]]|U|$5|N|O|P|C|$Q|V]]]]

Empty structs, as <a href="https://stackoverflow.com/users/281108/isbadawi">isbadawi</a> <a href="https://stackoverflow.com/questions/2632021/can-sizeof-return-0-zero/2632031#2632031">mentions</a>. Also gcc allows <a href="http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html" rel="nofollow noreferrer">arrays of 0 size</a>:

<pre><code>int a[0];
sizeof(a);
</code></pre>

EDIT: After seeing the MSDN link, I tried the empty struct in VS2005 and sizeof did return 1. I'm not sure if that's a VS bug or if the spec is somehow flexible about that sort of thing

blocks|key|1277721|text|在我看来，对于大小为0的结构，最好是sizeof返回0(本着c的精神)。但是，程序员在使用空结构的大小时必须小心。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277722|但这可能会造成问题。当定义此类结构的数组时，则|1277723|&arr1+==+&arr2+==+&arr|1277724|这让他们失去了身份。|1277725|我猜这并没有直接回答你的问题，不管它是可能的还是不可能的。嗯，这可能是可能的，取决于编译器。(正如Michael在上面的回答中所说的)。|1277726|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

in my view, it is better that sizeof returns 0 for a structure of size 0 (in the spirit of c). 
but then the programmer has to be careful when he takes the sizeof an empty struct.

but it may cause a problem.
when array of such structures is defined, then

&amp;arr[1] == &amp;arr[2] == &amp;arr[0]

which makes them lose their identities.

i guess this doesnt directly answer your question, whether it is possible or not.
well that may be possible depending on the compiler. (as said in Michael's answer above).

blocks|key|1063046|text|在C和C%2B%2B中，sizeof从不返回0。每次您看到sizeof的计算结果为0时，这都是一个与语言无关的特定编译器的错误/小故障/扩展。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1063047|entityMap^0|8|6|I|1|P|6|11|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]|$9|O|A|P|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|G|$]]

<code>sizeof</code> never returns <code>0</code> in C and in C++. Every time you see <code>sizeof</code> evaluating to <code>0</code> it is a bug/glitch/extension of a specific compiler that has nothing to do with the language.

blocks|key|1277819|text|我认为它在c中永远不会返回0，不允许有空结构。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277820|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|$]]

I think it never returns 0 in c , no empty structs is allowed

blocks|key|1063160|text|下面是一个测试，其中sizeof产生0|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1063161|#include+<stdio.h>

void+func(int+i)
{
++++++++int+vla[i];
++++++++printf+("%25u\n",(unsigned)sizeof+vla);
}


int+main(void)
{

++++++++func(0);
++++++++return+0;
}|code-block|syntax|javascript|1063162|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a test, where sizeof yields 0

<pre><code>#include &lt;stdio.h&gt;

void func(int i)
{
 int vla[i];
 printf ("%u\n",(unsigned)sizeof vla);
}


int main(void)
{

 func(0);
 return 0;
}
</code></pre>

blocks|key|1063281|text|typedef+struct+{
++int+:+0;
}+x;

x+x1;
x+x2;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1063282|在MSVC2010+(/Za+/Wall)下：|unstyled|1063283|sizeof(x)+==+4
&x1+!=+&x2|1063284|在GCC+(-ansi+-pedantic+-Wall)的带领下：|1063285|sizeof(x)+==+0
&x1+!=+&x2|1063286|也就是说，即使在GCC下它的大小为零，该结构的实例也有不同的地址。|1063287|ANSI+(C89和C99+-我还没看过C%2B%2B)说“应该可以唯一地表示对象的每个单独字节的地址。”对于零大小的对象，这似乎是模棱两可的，因为它可以说没有字节。|1063288|编辑:没有声明符但只有冒号和宽度的位域声明表示未命名的位域。作为这种情况的特例，宽度为0的位域表示不再将位域打包到放置前一个位域(如果有的话)的单元中。|1063289|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|V|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|M|3|N|5|F|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|F|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|F|7|12|8|@]|9|@]|A|$]]]|T|$]]

<pre><code>typedef struct {
 int : 0;
} x;

x x1;
x x2;
</code></pre>

Under MSVC 2010 (/Za /Wall):

<pre><code>sizeof(x) == 4
&amp;x1 != &amp;x2
</code></pre>

Under GCC (-ansi -pedantic -Wall) : 

<pre><code>sizeof(x) == 0
&amp;x1 != &amp;x2
</code></pre>

i.e. Even though under GCC it has zero size, instances of the struct have distinct addresses.

ANSI C (C89 and C99 - I haven't looked at C++) says "It shall be possible to express the address of each individual byte of an object uniquely." This seems ambiguous in the case of a zero-sized object, since it arguably has no bytes.

Edit: "A bit-field declaration with no declarator, but only a colon and a width, indicates an unnamed bit-field. As a special case of this, a bit-field with a width of 0 indicates that no further bit-field is to be packed into the unit in which the previous bit-field, if any, was placed."

blocks|key|1277985|text|如果你有这个：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1277986|struct+Foo+{};+
struct+Bar+{+Foo+v[];+}|code-block|syntax|javascript|1277987|g%2B%2B+-ansi返回sizeof(Bar)+==+0。clang+&+intel编译器也是如此。|offset|length|style|CODE|1277988|然而，这并不适用于gcc。我推断它是一个C%2B%2B扩展。|1277989|entityMap^0|0|0|0|9|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

If you have this :

<pre><code>struct Foo {}; 
struct Bar { Foo v[]; }
</code></pre>

<code>g++ -ansi</code> returns sizeof(Bar) == 0. As does the clang &amp; intel compiler.

However, this does not compile with gcc. I deduce it's a C++ extension.

blocks|key|1063346|text|struct+Empty+{
}+em;

struct+Zero+{
++++Empty+a[0];
}+zr;

printf("em=%25d\n",+sizeof(em));
printf("zr=%25d\n",+sizeof(zr));|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1063347|结果：|unstyled|1063348|em=1
zr=0|1063349|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>struct Empty {
} em;

struct Zero {
 Empty a[0];
} zr;

printf("em=%d\n", sizeof(em));
printf("zr=%d\n", sizeof(zr));
</code></pre>

Result:

<pre><code>em=1
zr=0
</code></pre>

Is it possible for the sizeof operator to ever return 0 (zero) in C or C++? If it is possible, is it correct from a standards point of view?

Can sizeof return 0 (zero)

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C或C++中，sizeof运算符有可能返回0(零)吗？如果可能，从标准的角度来看，它是正确的吗？

问sizeof能否返回0(零)
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