如何在Free Pascal中绑定EyeLink头文件中的函数指针宏常量？

我已经完成了EyeLink眼动系统sdl_expt.h/sdl2_expt.h头文件中CCDBS结构体和getExButtonStates函数指针类型的Free Pascal绑定，但不清楚如何绑定EXTERNAL_DEV_NONE、EXTERNAL_DEV_CEDRUS、EXTERNAL_DEV_SYS_KEYBOARD这三个宏常量，求指导。

原C头文件代码 #

typedef struct _CCDBS { // calibration control device button state structure
    void *userdata;   // user data passed in with enable_external_calibration_device
    char buttons[256];  // set button[i] to 1 for pressed 0 to released
    void *internal;   // for internal use.
}CCDBS;

typedef int (ELCALLBACK *getExButtonStates)(CCDBS *);  

#define EXTERNAL_DEV_NONE ((getExButtonStates)0)
#define EXTERNAL_DEV_CEDRUS ((getExButtonStates)1)
#define EXTERNAL_DEV_SYS_KEYBOARD ((getExButtonStates)2)

我的Free Pascal绑定代码 #

type
  PCCDBS = ^CCDBS;
  CCDBS = record
    userdata: Pointer;
    buttons: array[0..255] of Char;
    internal: Pointer;
  end;

  TGetExButtonStatesFunction = function (ccdbs: PCCDBS): Int32; stdcall;

  function getExButtonStates(ccdbs: PCCDBS): Int32; stdcall; external DLLNAME; 

解决方案 #

这三个宏本质是把整数0、1、2强制转换为getExButtonStates函数指针类型。在Free Pascal中，直接通过常量定义+类型强制转换就能实现等价绑定：

const
  EXTERNAL_DEV_NONE: TGetExButtonStatesFunction = TGetExButtonStatesFunction(0);
  EXTERNAL_DEV_CEDRUS: TGetExButtonStatesFunction = TGetExButtonStatesFunction(1);
  EXTERNAL_DEV_SYS_KEYBOARD: TGetExButtonStatesFunction = TGetExButtonStatesFunction(2);

注意事项 #

• 转换后的常量类型必须和目标参数类型匹配（即TGetExButtonStatesFunction），这样才能正确传入EyeLink的相关API（比如enable_external_calibration_device）。
• Free Pascal的类型强制转换逻辑和C语言一致，直接用目标类型包裹数值即可完成转换。

内容的提问来源于stack exchange，提问作者cpicanco