Olaf Dietrich写道：

我可能只是暂时（希望......）愚蠢，但是怎么能

我使用

（有符号/无符号）字符数组（以符合标准的方式）传递函数之间的函数指针？


例如：


我有一个函数：int（* func）（double，int）。


现在我我希望存储地址。这个函数是一个数组（足够大小）的字符，例如
，例如在

char func_addr [100]。 （我怎么能这样做？）

char func_addr [sizeof func];

memcpy（func_addr，& func，sizeof func） ;

最后我想在另一个

函数指针中使用这个地址：

new_func =（ int（*）（double，int））func_addr。

memcpy（& new_func，func_addr，sizeof new_func）;

这不起作用 - gcc抱怨：ISO C禁止转换

指向函数指针类型的对象指针。

那是因为你试图转换func_addr，在这种情况下

衰变为指向第一个char的指针那个数组，成为指向

a函数的指针。你想要它做的是解释那个

数组的内容，好像它是一个指向函数的指针。这种

转换的语法（安全）是：


new_func = *（int（**）（double，int））func_addr ;


这将func_addr从指向char数组的指针转换为

指向函数指针的指针，然后取消引用该指针，获取

a函数指针。不幸的是，这不是一个安全的方法来使用，因为不能保证func_addr正确对齐

持有这样的指针。如果func_addr

是指向动态分配的char数组的指针，或者如果func_addr

是具有相应函数指针类型的并集的一部分，则可以保证正确对齐。

James Kuyper< ja ********* @ verizon.net>：

Olaf Dietrich写道：

>现在我想存储地址。这个函数在一个数组（足够大小）的字符中，例如，在
char func_addr [100]。 （我怎么能这样做？）

char func_addr [sizeof func];

memcpy（func_addr，& func，sizeof func） ;

>最后我想在另一个
函数指针中使用这个地址：

memcpy（& new_func，func_addr，sizeof new_func）;

多么明显和简单......（甚至可以工作）。


非常感谢您的帮助

Olaf

10月22日13:10，o ... @ dtrx.de（Olaf Dietrich）写道：

我可能只是暂时（希望......）愚蠢，但怎么能

我使用数组
传递函数之间的函数指针
（签名/未签名）字符（符合标准的方式）？

你为什么要这样做？某种回调功能？

如果可以，***避免使用。


< snip>


-

Nick Keighley

I may just be temporarily (hopefully ...) stupid, but how can
I pass a function pointer between functions using an array of
(signed/unsigned) chars (in a standard-conforming way)?
E.g.:

I have a function: int (*func)(double, int).

Now I''d like to store the "address" of this function
in an array (of sufficient size) of chars, e.g. in
char func_addr[100]. (How can I do this?)

And finally I would like to use this address in another
function pointer:
new_func = (int (*)(double, int)) func_addr.

This doesn''t work - gcc complains: "ISO C forbids conversion
of object pointer to function pointer type".
Is there a way to store the data that constitutes the function
pointer in an array of chars (that need not have the size of
an object pointer)? And then to re-interpret this sequence of
bytes again as a function pointer?
Thanks for any suggestions
Olaf

Olaf Dietrich wrote:

I may just be temporarily (hopefully ...) stupid, but how can
I pass a function pointer between functions using an array of
(signed/unsigned) chars (in a standard-conforming way)?
E.g.:

I have a function: int (*func)(double, int).

Now I''d like to store the "address" of this function
in an array (of sufficient size) of chars, e.g. in
char func_addr[100]. (How can I do this?)

char func_addr[sizeof func];
memcpy(func_addr, &func, sizeof func);

And finally I would like to use this address in another
function pointer:
new_func = (int (*)(double, int)) func_addr.

memcpy(&new_func, func_addr, sizeof new_func);

This doesn''t work - gcc complains: "ISO C forbids conversion
of object pointer to function pointer type".

That''s because you''re trying to convert func_addr, which in this context
decays into a pointer to the first char of that array, into a pointer to
a function. What you want it to do is interpret the contents of that
array as if it were a pointer to a function. The syntax for such a
conversion (were it safe) would be:

new_func = *(int (**)(double, int)) func_addr;

This converts func_addr from a pointer to an array of char into a
pointer to a function pointer, then dereferences that pointer, obtaining
a function pointer. This is not, unfortunately, a safe approach to
use, because there''s no guarantee that func_addr is correctly aligned to
hold such a pointer. You could guarantee correct alignment if func_addr
were a pointer to a dynamically allocated array of char, or if func_addr
were part of a union with a the appropriate function pointer type.

James Kuyper <ja*********@verizon.net>:

Olaf Dietrich wrote:

>Now I''d like to store the "address" of this function
in an array (of sufficient size) of chars, e.g. in
char func_addr[100]. (How can I do this?)

char func_addr[sizeof func];
memcpy(func_addr, &func, sizeof func);

>And finally I would like to use this address in another
function pointer:

memcpy(&new_func, func_addr, sizeof new_func);

How obvious and simple ... (and it even works).

Thank you very much for your help
Olaf

On 22 Oct, 13:10, o...@dtrx.de (Olaf Dietrich) wrote:

I may just be temporarily (hopefully ...) stupid, but how can
I pass a function pointer between functions using an array of
(signed/unsigned) chars (in a standard-conforming way)?

why do you want to do this? Some sort of callback function?
It''s best avoided if you can.

<snip>

--
Nick Keighley