这是有效的C语句吗？ [英] Is this valid C statement?
问题描述
亲爱的，
根据标准，这是有效的：
char TmpPtrWriteBuffer [1000];
void * PtrWriteBuffer =（void *）TmpPtrWriteBuffer;
我和我的同事们辩论说，任何事情都无法解释为
void *虽然反过来是真的。但他们说这是有效的。
我不能同意他们的有效解释。任何C
标准专家都能澄清这一点吗？
问候，
s.subbarayan
Dear all,
According to standards is this valid:
char TmpPtrWriteBuffer[1000];
void* PtrWriteBuffer =(void*) TmpPtrWriteBuffer;
I had a debate with my colleagues that anything cant be typecasted to
void* though the reverse is true.But they said this is valid.
I just can''t agree with them with out a valid explaination.Can any C
standard experts clarify me this?
Regards,
s.subbarayan
推荐答案
s.subbarayan< s _ *** *******@rediffmail.com>潦草地写道：
s.subbarayan <s_**********@rediffmail.com> scribbled the following:
亲爱的，
根据标准，这是有效的：
char TmpPtrWriteBuffer [1000];
void * PtrWriteBuffer =（void *）TmpPtrWriteBuffer;
我和我的同事们辩论说，任何事情都不能说是无效*虽然反过来也是如此。但是他们说这是有效的。
我不能同意他们的意见可以解释一下有效的解释。任何C标准专家都能澄清一下这个吗？
Dear all,
According to standards is this valid: char TmpPtrWriteBuffer[1000];
void* PtrWriteBuffer =(void*) TmpPtrWriteBuffer; I had a debate with my colleagues that anything cant be typecasted to
void* though the reverse is true.But they said this is valid.
I just can''t agree with them with out a valid explaination.Can any C
standard experts clarify me this?
你是对的。指向任何东西的指针都可以分配到
void *，即使没有强制转换也是如此。但是，这并不意味着任何void *
总能安全地分配到任何其他指针类型中。可能
是对齐冲突或其他可能依赖于实现的问题
问题。
例如，以下代码通常不起作用：
char * cp;
int * ip;
void * vp;
if（cp = malloc（1000））{
vp = cp + 1;
ip = vp;
}
即使代码编译得很好，也可能在运行时导致错误，因为行ip = vp;将指向不正确的指针值分配给int指针。 （假设sizeof（int）> 1。）
-
/ - Joona Palaste（pa ***** @ cc。 helsinki.fi）-------------芬兰-------- \
\-- http://www.helsinki.fi/~palaste --------------- ------规则！ -------- /
"犯错是人。要真正搞砸了一台电脑。
- Anon
You are right on this one. A pointer to anything can be assigned into a
void *, even without a cast. However, this does not mean that any void *
can always safely be assigned into any other pointer type. There might
be alignment conflicts or other, possibly implementation-dependent,
issues.
For example the following code will usually not work:
char *cp;
int *ip;
void *vp;
if (cp=malloc(1000)) {
vp = cp+1;
ip = vp;
}
Even though the code compiles nicely, it might cause errors at run-time,
because the line ip = vp; assigns a pointer value that is not properly
aligned to int into a int pointer. (This is assuming sizeof(int)>1.)
--
/-- Joona Palaste (pa*****@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"To err is human. To really louse things up takes a computer."
- Anon
" s.subbarayan" < S _ ********** @ rediffmail.com>在留言中写道
news：c3 ************************** @ posting.google.c om ...
"s.subbarayan" <s_**********@rediffmail.com> wrote in message
news:c3**************************@posting.google.c om...
亲爱的，
根据标准，这是有效的：
char TmpPtrWriteBuffer [1000];
void * PtrWriteBuffer =（void *）TmpPtrWriteBuffer;
我与同事们辩论说，任何事情都不能说是无效*虽然反过来也是如此。但是他们说这是有效的。
我就是不能如果有任何C
标准专家对此进行澄清，请与他们达成一致。
Dear all,
According to standards is this valid:
char TmpPtrWriteBuffer[1000];
void* PtrWriteBuffer =(void*) TmpPtrWriteBuffer;
I had a debate with my colleagues that anything cant be typecasted to
void* though the reverse is true.But they said this is valid.
I just can''t agree with them with out a valid explaination.Can any C
standard experts clarify me this?
你的同事是对的。类型（void *）
的指针具有相同的对齐要求和内部表示
作为（char *）。符号TmpPtrWriteBuffer恶化
键入（char *），因此将其转换为（void *）并不会损害指针值的完整性。目标符号
" PtrWriteBuffer"有类型（void *），所以从（void *）到（void *）的赋值
也是有效的。
Your colleagues are correct. A pointer of type (void*)
has the same alignment requirements and internal representation
as a (char*). The symbol "TmpPtrWriteBuffer" deteriorates
to type (char*), so casting it to (void*) doesn''t harm
the integrity of the pointer value. The target symbol
"PtrWriteBuffer" has type (void*), so the assignment
from (void*) to (void*) is also valid.
Joona I Palaste < PA ***** @ cc.helsinki.fi>潦草地写道：
Joona I Palaste <pa*****@cc.helsinki.fi> scribbled the following:
s.subbarayan< s _ ********** @ rediffmail.com>潦草地写道：
s.subbarayan <s_**********@rediffmail.com> scribbled the following:
亲爱的，
根据标准，这是有效的：
char TmpPtrWriteBuffer [1000];
void * PtrWriteBuffer =（void *）TmpPtrWriteBuffer;
我和我的同事们辩论说，任何事情都不能说是无效*虽然反过来也是如此。但是他们说这是有效的。
我不能同意他们的意见有效的解释。任何C
标准专家都能澄清这一点吗？
Dear all,
According to standards is this valid: char TmpPtrWriteBuffer[1000];
void* PtrWriteBuffer =(void*) TmpPtrWriteBuffer; I had a debate with my colleagues that anything cant be typecasted to
void* though the reverse is true.But they said this is valid.
I just can''t agree with them with out a valid explaination.Can any C
standard experts clarify me this?
你是对的。指向任何东西的指针都可以分配到
void *中，即使没有强制转换也是如此。但是，这并不意味着任何void *
始终可以安全地分配给任何其他指针类型。可能存在对齐冲突或其他可能依赖于实现的问题。
例如，以下代码通常不起作用：
char * cp;
int * ip;
void * vp;
if（cp = malloc（1000））{
vp = cp + 1;
ip = vp;
}
即使代码编译得很好，也可能在运行时导致错误，因为行ip = vp;将未正确对齐int的指针值分配给int指针。 （假设sizeof（int）> 1。）
You are right on this one. A pointer to anything can be assigned into a
void *, even without a cast. However, this does not mean that any void *
can always safely be assigned into any other pointer type. There might
be alignment conflicts or other, possibly implementation-dependent,
issues.
For example the following code will usually not work:
char *cp;
int *ip;
void *vp;
if (cp=malloc(1000)) {
vp = cp+1;
ip = vp;
}
Even though the code compiles nicely, it might cause errors at run-time,
because the line ip = vp; assigns a pointer value that is not properly
aligned to int into a int pointer. (This is assuming sizeof(int)>1.)
对不起，在阅读了xarax的回复之后，我发现我已经
回答了错误的问题。是的，你的同事是正确的
a指向任何东西的指针都可以分配给void *有或没有演员。
正如我上面所示，分配回到其他方向将
不一定有效。
-
/ - Joona Palaste（pa ***** @ cc.helsinki.fi）-------------芬兰-------- \
\-- http://www.helsinki.fi/~palaste ------------- --------规则！ -------- /
当一个男人对一个女人说脏话时，那就是性骚扰。当一个女人对男人说脏话时，那是'每分钟14.99美元+本地电话费！'
- Ruben Stiller
Sorry, after having read xarax''s reply, I have found out that I have
answered the wrong question. Yes, your colleagues are correct in that
a pointer to anything can be assigned to void * with or without a cast.
As I have shown above, the assignment back in the other direction will
not necessarily work.
--
/-- Joona Palaste (pa*****@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"When a man talks dirty to a woman, that''s sexual harassment. When a woman talks
dirty to a man, that''s 14.99 per minute + local telephone charges!"
- Ruben Stiller
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