指定C ++实例方法到全球函数指针？ [英] Assign C++ instance method to a global-function-pointer?

问题描述

问候，

我的项目结构如下：

\- base  (C static library)
     callbacks.h
     callbacks.c
     paint_node.c
     . 
     .
     * libBase.a

\-app (C++ application)
     main.cpp

在C库'基地'，我已经宣布全球函数指针为：

In C library 'base' , I have declared global-function-pointer as:

在singleheader文件

in singleheader file

callbacks.h

callbacks.h

#ifndef CALLBACKS_H_
#define CALLBACKS_H_

extern void (*putPixelCallBack)();
extern void (*putImageCallBack)();

#endif /* CALLBACKS_H_ */

在单个C文件中它们被初始化为

in single C file they are initialized as

的callbacks.c

callbacks.c

#include "callbacks.h"
void (*putPixelCallBack)();
void (*putImageCallBack)();

其他的C文件访问此回调函数为：

Other C files access this callback-functions as:

paint_node.c

paint_node.c

#include "callbacks.h"
void paint_node(node *node,int index){

  //Call callbackfunction
  .
  .

  putPixelCallBack(node->x,node->y,index);
}

我编译这些C文件，并生成一个静态库libBase.a

I compile these C files and generate a static library 'libBase.a'

然后在C ++应用程序，

Then in C++ application,

我想C ++实例方法分配到此全局函数指针：

I want to assign C++ instance method to this global function-pointer:

我不喜欢的东西如下：

在Sacm.cpp文件

in Sacm.cpp file

#include "Sacm.h"

extern void (*putPixelCallBack)();
extern void (*putImageCallBack)();

void Sacm::doDetection()
{
  putPixelCallBack=(void(*)())&paintPixel;
  //call somefunctions in 'libBase' C library

}

void Sacm::paintPixel(int x,int y,int index)
{
 qpainter.begin(this);
 qpainter.drawPoint(x,y);
 qpainter.end();
}

但是，当编译它给人的错误：

But when compiling it gives the error:

sacmtest.cpp：在成员函数'无效
  SACM :: doDetection（）：
  sacmtest.cpp：113：错误：ISO C ++
  禁止服用的地址
  不合格或括号
  非静态成员函数，以形成一个
  成员函数指针。说
  '和; SACM :: paintPixel'sacmtest.cpp：113：
  错误：从'转换无效
  （SACM :: ）（INT，INT，INT）'到'无效
  （的）（）

sacmtest.cpp: In member function ‘void Sacm::doDetection()’: sacmtest.cpp:113: error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function. Say ‘&Sacm::paintPixel’ sacmtest.cpp:113: error: converting from ‘void (Sacm::)(int, int, int)’ to ‘void ()()’

任何提示？

推荐答案

这是C ++的常见问题，的 33.2 。这不起作用，因为指针不与特定对象实例相关联。该解决方案给出那里，创建一个使用特殊对象的全局函数：

This is the C++ FAQ, 33.2. This doesn't work, because the pointer isn't associated with a particular object instance. The solution is given there too, create a global function that uses a particular object:

 Sacm* sacm_global;

 void sacm_global_paintPixel(int x,int y,int index)
 {
   sacm_global->paintPixel(x, y, index);
 }

void Sacm::doDetection()
{
  putPixelCallBack = &sacm_global_paintPixel;
  //call somefunctions in 'libBase' C library
}

您必须以某种方式设置全局变量正常。

You have to somehow setup the global variable properly.

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