typedef用于转换函数指针 [英] typedef Used to Cast Function Pointers
问题描述
是否可以使用typedef来转换函数指针？我想我在WINGs src中看到了这个
; grep for''（hashFunc）''。到目前为止，尝试
使用typedef来转换函数指针，以便将返回值
float更改为float似乎不起作用;我相信它就像是
这个：
typedef int（* foo）（int）;
function_ptr_bar =（foo）function_that_returns_float;
Is is possible to use typedefs to cast function pointers? I think I
saw this in the WINGs src; grep for ''(hashFunc)''. So far, trying to
use a typedef to cast function pointers so that a return value of
float is changed to float seems not to work; I belive it was like
this:
typedef int (*foo) (int);
function_ptr_bar = (foo)function_that_returns_float;
推荐答案
Barbrawl McBribe写道：
Barbrawl McBribe wrote:
是否可以使用typedef来cast函数指针？
只有一个演员表达可以用来演员。
我想我在WINGs src中看到了这个; grep for''（hashFunc）''。到目前为止，尝试使用typedef来转换函数指针，以便将返回值
float更改为float似乎不起作用;我相信它就像
这样：
typedef int（* foo）（int）;
这将foo声明为类型为指向函数的指针的别名，类型为int，返回int" ;.
function_ptr_bar =（foo）function_that_returns_float;
Is is possible to use typedefs to cast function pointers?
Only a cast expression can be used to cast.
I think I
saw this in the WINGs src; grep for ''(hashFunc)''. So far, trying to
use a typedef to cast function pointers so that a return value of
float is changed to float seems not to work; I belive it was like
this:
typedef int (*foo) (int);
This declares foo as an alias for type "pointer to function taking 1
argument of type int and returning int".
function_ptr_bar = (foo)function_that_returns_float;
这使用强制转换表达式从一种类型转换为另一种类型。我不认为
相信你可以通过生成的指针安全地调用该函数
，除非它首先被转换回正确的类型。
-Kevin
-
我的电子邮件地址有效，但会定期更改。
要联系我，请使用地址来自最近的帖子。
This uses a cast expression to convert from one type to another. I don''t
believe you can safely call the function through the resulting pointer
unless it is first cast back to the correct type.
-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.
fi **** ***@thelinuxlink.net （Barbrawl McBribe）写道：
fi*******@thelinuxlink.net (Barbrawl McBribe) writes:
是否可以使用typedef来转换函数指针？我想我在WINGs src看到了这个; grep for''（hashFunc）''。到目前为止，尝试使用typedef来转换函数指针，以便将返回值
float更改为float似乎不起作用;我相信它就像
这样：
typedef int（* foo）（int）;
function_ptr_bar =（foo）function_that_returns_float;
Is is possible to use typedefs to cast function pointers? I think I
saw this in the WINGs src; grep for ''(hashFunc)''. So far, trying to
use a typedef to cast function pointers so that a return value of
float is changed to float seems not to work; I belive it was like
this:
typedef int (*foo) (int);
function_ptr_bar = (foo)function_that_returns_float;
我认为你的意思是所以浮动的返回值改为
int。
为什么你想要这样做吗？你可以使它工作，但是它是非常不安全和不便携的。基本上，你正试图向编译器撒谎。充其量，你会调用function_that_returns_float（）
并将其结果视为int（不是数字转换，而是对位进行重新解释）。在最坏的情况下，调用约定将会不同，并且会发生任意不好的事情，从获得无效的垃圾到崩溃你的程序。
-
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://www.sdsc.edu/~kst>
Schroedinger做莎士比亚：要*和*不要
（注意新的e邮件地址）
I presume you mean "so that a return value of float is changed to
int".
Why would you want to do this? You can probably make it work, but
it''s extremely unsafe and non-portable. Basically, you''re trying to
lie to the compiler. At best, you''ll call function_that_returns_float()
and treat its result as an int (not a numeric conversion, but a
reinterpretation of the bits). At worst, the calling conventions will
differ, and arbitrarily bad things will happen, from getting
meaningless garbage to crashing your program.
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://www.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"
(Note new e-mail address)
Keith Thompson写道：
Keith Thompson wrote:
fi ******* @ thelinuxlink.net （Barbrawl McBribe）写道：
fi*******@thelinuxlink.net (Barbrawl McBribe) writes:
是可以使用typedef来转换函数指针吗？我想我在WINGs src看到了这个; grep for''（hashFunc）''。到目前为止，尝试使用typedef来转换函数指针，以便将返回值
float更改为float似乎不起作用;我相信它就像
这样：
typedef int（* foo）（int）;
function_ptr_bar =（foo）function_that_returns_float;
Is is possible to use typedefs to cast function pointers? I think I
saw this in the WINGs src; grep for ''(hashFunc)''. So far, trying to
use a typedef to cast function pointers so that a return value of
float is changed to float seems not to work; I belive it was like
this:
typedef int (*foo) (int);
function_ptr_bar = (foo)function_that_returns_float;
我认为你的意思是所以浮动的返回值改为
int。
你为什么要这样做？你可以使它工作，但它是非常不安全和不便携的。基本上，你试图欺骗编译器。充其量，你会调用function_that_returns_float（）
并将其结果视为int（不是数字转换，而是对位的重新解释）。在最坏的情况下，调用约定会有所不同，并且会发生任意不好的事情，从获得无意义的垃圾到崩溃你的程序。
I presume you mean "so that a return value of float is changed to
int".
Why would you want to do this? You can probably make it work, but
it''s extremely unsafe and non-portable. Basically, you''re trying to
lie to the compiler. At best, you''ll call function_that_returns_float()
and treat its result as an int (not a numeric conversion, but a
reinterpretation of the bits). At worst, the calling conventions will
differ, and arbitrarily bad things will happen, from getting
meaningless garbage to crashing your program.
标准明确地将其称为未定义行为。
来自6.3.2.3.8
"指向一种类型函数的指针可以转换为
a指向另一种类型的函数并再次返回;
结果应该等于原始指针。
如果转换指针用于调用一个函数的
类型与指向类型不兼容，
行为未定义。
-
Al Bowers
美国佛罗里达州坦帕市
mailto： xa ****** @ myrapidsys.com （删除x发送电子邮件）
http://www.geocities.com/abowers822/
The Standard explicitly calls it Undefined Behavior.
From 6.3.2.3.8
"A pointer to a function of one type may be converted to
a pointer to a function of another type and back again;
the result shall compare equal to the original pointer.
If a converted pointer is used to call a function whose
type is not compatible with the pointed-to type, the
behavior is undefined."
--
Al Bowers
Tampa, Fl USA
mailto: xa******@myrapidsys.com (remove the x to send email)
http://www.geocities.com/abowers822/
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