外部“C” struct - >类 [英] extern "C" struct -> class

问题描述

以下程序是否符合标准？我用一些

编译器编译它并没有产生任何错误或警告，但这不是一个

演示。


有罪的部分是声明：


externC struct X;


然后被定义为：


class X {};


我知道''extern'C"''只改变链接规范，但

转发C ++中的声明/通常/不允许使用不同的

class-keys。

问候，

Daniele。

>>>>>>>>>>>>>>>>>

/ *声明* /


externC {

struct X;


X * new_X（）;

void delete_X（X *）;

}


/ * definitions * /


class X {};

externC ; {


X * new_X（）

{

返回新的X（）;

}


void delete_X（X * p）

{

删除p;

}


} // extern" C"


int main（）

{

X * p = new_X（）;

delete_X（p）;

返回0;

}


<<<<<<<<<<<<<<<<<

解决方案

Daniele Benegiamo写道：

以下程序是否符合标准？我已经用一些
编译器编译了它，没有产生任何错误或警告，但这不是一个演示。

有罪的部分是声明：

externC结构X;

然后定义为：

类X {};

我知道''extern'C"''只更改链接规范，但是用C ++转发声明/通常/不允许使用不同的类键。

为了安全起见，我将从externC

struct派生一个类。


externC struct X {...};


class X_impl：public X

{

// ...

};

Maxim Yegorushkin写道：

为了安全起见，我将派出一个班级来自externC
结构。

externC struct X {...};

类X_impl：public X
{
// ...
};

但是这样功能的实现变得更加昂贵

（作为维护和bug的可能性），因为它需要转换为

正常工作。例如：


externC struct X {/ * empty * /};


class X_impl：public X

{

// ... < br $>
};


extern" C"

{


void foo（ X * p）

{

X_impl * p2 = static_cast< X_impl *> （p）;

// ...

}


void delete_X（X * p）

{

删除static_cast< X_impl *> （p）;

}


} // externC


然而这是可能的解。谢谢你的回复。


Daniele

Daniele Benegiamo写道：


[]

但是这样功能的实现变得更加昂贵（因为维护和bug的可能性），因为它需要转换为
工作正常。例如：

嗯，编程很昂贵，需要打字。

Is the following program standard-compliant? I''ve compiled it with some
compilers and no errors or warnings are produced, but this is not a
demonstration.

The "incriminated" part is the declaration:

extern "C" struct X;

that is then defined as:

class X {};

I know that ''extern "C"'' change only the linkage specification, but
forwarding declarations in C++ /usually/ don''t allow usage of different
class-keys.
Regards,
Daniele.

>>>>>>>>>>>>>>>>>

/* declarations */

extern "C" {
struct X;

X * new_X ();
void delete_X (X *);
}

/* definitions */

class X {};
extern "C" {

X * new_X ()
{
return new X ();
}

void delete_X (X * p)
{
delete p;
}

} // extern "C"

int main ()
{
X * p = new_X ();
delete_X (p);
return 0;
}

<<<<<<<<<<<<<<<<

解决方案

Daniele Benegiamo wrote:

Is the following program standard-compliant? I''ve compiled it with some
compilers and no errors or warnings are produced, but this is not a
demonstration.

The "incriminated" part is the declaration:

extern "C" struct X;

that is then defined as:

class X {};

I know that ''extern "C"'' change only the linkage specification, but
forwarding declarations in C++ /usually/ don''t allow usage of different
class-keys.

To be on the safe side I would derive a class from an extern "C"
struct.

extern "C" struct X { ... };

class X_impl : public X
{
// ...
};

Maxim Yegorushkin wrote:

To be on the safe side I would derive a class from an extern "C"
struct.

extern "C" struct X { ... };

class X_impl : public X
{
// ...
};

But in this way the implementation of functions become more expensive
(as maintenance and probability of bugs), because it needs casting to
works properly. E.g.:

extern "C" struct X { /* empty */ };

class X_impl : public X
{
// ...
};

extern "C"
{

void foo (X * p)
{
X_impl * p2 = static_cast<X_impl *> (p);
// ...
}

void delete_X (X * p)
{
delete static_cast<X_impl *> (p);
}

} // extern "C"

However this is a possible solution. Thanks for your reply.

Daniele

Daniele Benegiamo wrote:

[]

But in this way the implementation of functions become more expensive
(as maintenance and probability of bugs), because it needs casting to
works properly. E.g.:

Well, programming is expensive, it requires typing.

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