另一个问题 [英] Another sizeof question
问题描述
如果已经报道，请原谅。
给予
char x [42];
是
sizeof（x [999]）
任何类型的错误？如果是这样，既然没有评估表达式，那么如何检测到这样的错误？b
如果声明是
int n = 42;
char x [n];
？
- Richard
-
"考虑到需要多达32个字符某些字母表中的
" - 1963年的X3.4。
Please excuse me if this has already been covered.
Given
char x[42];
is
sizeof(x[999])
any kind of error? If so, since the expression is not evaluated, how
would such an error be detected? What if the declaration was
int n = 42;
char x[n];
?
-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
推荐答案
ri ***** @ cogsci.ed.ac.uk （Richard Tobin）写道：
ri*****@cogsci.ed.ac.uk (Richard Tobin) writes:
如果已经涵盖，请原谅我。
给定
char x [42];
是
sizeof（x [999]）
任何类型的错误？
Please excuse me if this has already been covered.
Given
char x[42];
is
sizeof(x[999])
any kind of error?
[...]
我相信它完全有效，而且必须收益1.
x [999]相当于*（x + 999）。添加会调用未定义的
行为，但前提是它已被评估。
我认为没有更多理由
sizeof（ x [999]）
调用UB而不是
if（0）{
x [999];
}
这样做。
-
Keith Thompson（The_Other_Keith） ks *** @ mib.org < http://www.ghoti.net/~kst>
圣地亚哥超级计算机中心< * < http://users.sdsc.edu/~kst>
"我们必须做点什么。这是事情。因此，我们必须这样做。
- Antony Jay和Jonathan Lynn，是部长
[...]
I believe it''s perfectly valid, and must yield 1.
x[999] is equivalent to *(x+999). The addition would invoke undefined
behavior, but only if it were evaluated.
I see no more reason for
sizeof(x[999])
to invoke UB than for
if (0) {
x[999];
}
to do so.
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <* <http://users.sdsc.edu/~kst>
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
9月19日，3日：09：00，Keith Thompson< ks ... @ mib.orgwrote：
On Sep 19, 3:09 am, Keith Thompson <ks...@mib.orgwrote:
我相信它完全有效，而且必须产生1个。
x [999]相当于*（x + 999）。添加会调用未定义的
行为，但前提是它已被评估。
我认为没有更多理由
sizeof（ x [999]）
调用UB而不是
if（0）{
x [999];
}
这样做。
I believe it''s perfectly valid, and must yield 1.
x[999] is equivalent to *(x+999). The addition would invoke undefined
behavior, but only if it were evaluated.
I see no more reason for
sizeof(x[999])
to invoke UB than for
if (0) {
x[999];
}
to do so.
真的一定很好。类似的情况就是这个，可以在每个人的代码中找到数以万计的时间::
某事* p;
p = malloc（sizeof（* p））;
这是建议的分配内存的习惯用法，以及表达式
* p本身将像x [999]一样调用未定义的行为。这是好b $ b罚款，因为* p未被评估。
It really must be fine. A similar situation is this one, which can be
found gazillion times in everyone''s code::
something* p;
p = malloc (sizeof (*p));
This is the recommended idiom to allocate memory, and the expression
*p on its own would invoke undefined behaviour just like x[999]. It''s
fine because *p is not evaluated.
2007年9月19日星期三00:16:49 +0000，Richard托宾写道：
On Wed, 19 Sep 2007 00:16:49 +0000, Richard Tobin wrote:
如果已经报道，请原谅我。
鉴于
char x [42];
是
sizeof（x [999]）
任何类型的错误？如果是这样，既然没有评估表达式，那么如何检测到这样的错误？b
如果声明是
int n = 42;
char x [n];
Please excuse me if this has already been covered.
Given
char x[42];
is
sizeof(x[999])
any kind of error? If so, since the expression is not evaluated, how
would such an error be detected? What if the declaration was
int n = 42;
char x[n];
即使在这种情况下，x'的类型是VLA，但x [999]的类型是char，
因此它不会被sizeof评估。
-
Army1987（将NOSPAM替换为email）
如果你是从Windows机器发送电子邮件，请关闭微软的
傻瓜??智能行情？特征。这样你就可以避免通过你的邮件洒垃圾
字符了。 - Eric S. Raymond和Rick Moen
Even in this case, x''s type is a VLA, but x[999]''s type is char,
so it is not evaluated by sizeof.
--
Army1987 (Replace "NOSPAM" with "email")
If you''re sending e-mail from a Windows machine, turn off Microsoft''s
stupid a??Smart Quotesa?? feature. This is so you''ll avoid sprinkling garbage
characters through your mail. -- Eric S. Raymond and Rick Moen
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