将函数指针转换为void * [英] cast function pointer to void*
问题描述
*希望这个帖子不违反这个组的规则*
我在GNOME的glib-2.12源代码中找到了以下代码：
/ *在gclosure.c * /
GClosure *
g_cclosure_new（GCallback callback_func，
gpointer user_data ，
GClosureNotify destroy_data）
{
......
/ *（（GCClosure *）闭包） - >回调类型为gpointer * /
（（GCClosure *）闭包） - > callback =（gpointer）callback_func;
}
这里将GCallback转换为gpointer类型。
GCallback和gpointer的定义如下：
typedef void（* GCallback）（void）; / * in gclosure.h * /
typedef void * gpointer; / *在gtypes.h * /
因此结果是a（void（*）（void））被强制转换为（void *）。然而，对这个组和c99标准的搜索
表示向void指针投射
函数指针是未定义的行为。我想知道
是否更适合滑动练习。
WaterWalk写道：
< blockquote class =post_quotes>
*希望这个帖子不违反这个组的规则*
我在GNOME'中发现了以下代码glib-2.12来源：
[...]
因此结果是a（void（*）（void））被强制转换为（void *）。然而，对这个组和c99标准的搜索
表示向void指针投射
函数指针是未定义的行为。
这是违反约束的行为，实际上意味着它可能无法编译，或者
如果编译，/整个/程序超出了
C标准的范围（即使转换实际上从未执行过）。
我想知道是否
滑稽练习更可取。
优先购买什么？在标准C中根本没有办法可靠地将
转换为对象指针的函数指针，所以如果有一个
这样做的正当理由（我不是知道这里是否有充分的理由
），必须使用特定于实现的扩展来完成。
" ; WaterWalk" < to ******** @ 163.comwrote：
*希望这个帖子不违反这个组的规则*
代码是偏离主题的，但你问的问题 - 基本上，
_is_这个ISO C - 是关于主题的。
/ *在gclosure.c * /
GClosure *
g_cclosure_new（GCallback callback_func，
gpointer user_data，
GClosureNotify destroy_data）
{
......
/ *（（GCClosure *）闭包） - >回调类型为gpointer * /
（（GCClosure *）闭包） - > callback =（gpointer）callback_func;
}
这里将GCallback转换为gpointer类型。
GCallback和gpointer的定义如下：
typedef void（* GCallback）（void）; / * in gclosure.h * /
typedef void * gpointer; / *在gtypes.h * /
因此结果是a（void（*）（void））被强制转换为（void *）。然而，对这个组和c99标准的搜索
表示向void指针投射
函数指针是未定义的行为。我想知道
滑稽练习是否更可取。
是的，它是未定义的行为;因此，不，这是不可取的。
也没有必要，因为ISO C要求所有功能指针
类型可以相互转换没有损失
信息。
Richard
Harald van D？3k写道：
WaterWalk写道：
*希望这个帖子不违反这个组的规则*
我在GNOME的glib-2.12源代码中找到了以下代码：
[...]
所以结果是a（void（*）（void））被强制转换为（void *）。然而，对这个组和c99标准的搜索
表示向void指针投射
函数指针是未定义的行为。
这是违反约束的行为，实际上意味着它可能无法编译，或者如果它编译，则为/ b $ b，/整个/程序超出了
C标准的范围（即使转换永远不会被执行）。
实际上......我知道它被多个
编译器视为违反约束，但我似乎无法理解找到标准中的任何措辞
这样说。如果有人能说出来，我会很感激。
*Hope this thread doesn''t violate this group''s rule*
I found the following code in the GNOME''s glib-2.12 source:
/* In gclosure.c */
GClosure*
g_cclosure_new (GCallback callback_func,
gpointer user_data,
GClosureNotify destroy_data)
{
......
/* ((GCClosure*) closure)->callback is of type gpointer */
((GCClosure*) closure)->callback = (gpointer) callback_func;
}
Here a GCallback is cast to a gpointer type. The definition of
GCallback and gpointer are as follows:
typedef void (*GCallback) (void); /* in gclosure.h */
typedef void* gpointer; /* in gtypes.h */
So the result is that a (void (*)(void)) is cast to (void*). However a
search of this group and c99 standard indicates that casting a
function pointer to a void pointer is undefined behavior. I wonder if
the glib practice is preferable.
WaterWalk wrote:*Hope this thread doesn''t violate this group''s rule*
I found the following code in the GNOME''s glib-2.12 source:
[...]
So the result is that a (void (*)(void)) is cast to (void*). However a
search of this group and c99 standard indicates that casting a
function pointer to a void pointer is undefined behavior.It''s a constraint violation, actually, meaning it might not compile, or
if it does compile, the /entire/ program is outside of the scope of the
C standard (even if the conversion would never actually be performed).
I wonder if
the glib practice is preferable.Preferable to what? There''s simply no way in standard C to reliably
convert function pointers to object pointers, so if there is a
legitimate reason to do so (I don''t know if there is a good reason
here), it must be done using an implementation-specific extension.
"WaterWalk" <to********@163.comwrote:
*Hope this thread doesn''t violate this group''s rule*The code is off-topic, but the question you ask about it - basically,
_is_ this ISO C - is on-topic.
/* In gclosure.c */
GClosure*
g_cclosure_new (GCallback callback_func,
gpointer user_data,
GClosureNotify destroy_data)
{
......
/* ((GCClosure*) closure)->callback is of type gpointer */
((GCClosure*) closure)->callback = (gpointer) callback_func;
}
Here a GCallback is cast to a gpointer type. The definition of
GCallback and gpointer are as follows:
typedef void (*GCallback) (void); /* in gclosure.h */
typedef void* gpointer; /* in gtypes.h */
So the result is that a (void (*)(void)) is cast to (void*). However a
search of this group and c99 standard indicates that casting a
function pointer to a void pointer is undefined behavior. I wonder if
the glib practice is preferable.Yes, it''s undefined behaviour; and therefore, no, it''s not preferable.
Nor is it necessary, since ISO C requires that all function pointer
types can be converted to and from one another without loss of
information.
Richard
Harald van D?3k wrote:WaterWalk wrote:*Hope this thread doesn''t violate this group''s rule*
I found the following code in the GNOME''s glib-2.12 source:
[...]
So the result is that a (void (*)(void)) is cast to (void*). However a
search of this group and c99 standard indicates that casting a
function pointer to a void pointer is undefined behavior.
It''s a constraint violation, actually, meaning it might not compile, or
if it does compile, the /entire/ program is outside of the scope of the
C standard (even if the conversion would never actually be performed).Actually... I know it''s treated as a constraint violation by multiple
compilers, but I can''t seem to find any wording in the standard that
says so. I''d appreciate it if anyone could point it out.
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