Swig：包装全局静态常量时出现语法错误

Posted 2023-02-23

【中文标题】Swig：包装全局静态常量时出现语法错误

【英文标题】：Swig: syntax error when wrapping global static constants

【发布时间】：2019-05-30 12:02:53

【问题描述】：

当我尝试包装以下代码时：

enum VehicleSide 
    LEFT = 0,  ///< left side of vehicle is always 0
    RIGHT = 1  ///< right side of vehicle is always 1
;

/// Class to encode the ID of a vehicle wheel.
/// By convention, wheels are counted front to rear and left to right. In other
/// words, for a vehicle with 2 axles, the order is: front-left, front-right,
/// rear-left, rear-right.
class WheelID 
  public:
    WheelID(int id) : m_id(id), m_axle(id / 2), m_side(VehicleSide(id % 2)) 
    WheelID(int axle, VehicleSide side) : m_id(2 * axle + side), m_axle(axle), m_side(side) 

    /// Return the wheel ID.
    int id() const  return m_id; 

    /// Return the axle index for this wheel ID.
    /// Axles are counted from the front of the vehicle.
    int axle() const  return m_axle; 

    /// Return the side for this wheel ID.
    /// By convention, left is 0 and right is 1.
    VehicleSide side() const  return m_side; 

  private:
    int m_id;            ///< wheel ID
    int m_axle;          ///< axle index (counted from the front)
    VehicleSide m_side;  ///< vehicle side (LEFT: 0, RIGHT: 1)
;

/// Global constant wheel IDs for the common topology of a 2-axle vehicle.
static const WheelID FRONT_LEFT(0, LEFT);
static const WheelID FRONT_RIGHT(0, RIGHT);
static const WheelID REAR_LEFT(1, LEFT);
static const WheelID REAR_RIGHT(1, RIGHT);

我在 static const WheelID FRONT_LEFT(0, LEFT); 处收到“输入语法错误”。 在接口文件上，我只是在相应的标题上使用 %include。 我不知道是什么导致了错误，因此感谢您提供任何帮助，但我不想编辑标题。 谢谢

编辑： 删除 static 关键字无济于事

【参考方案1】：

显示您的 SWIG .i 文件会有所帮助，但原因可能是您已将类的实例放在头文件中。我看到您不想编辑标题，但是 .h 文件应该 extern 类实例，并且定义应该在 .cpp 文件中；否则，如果文件包含在两个不同的 .cpp 文件中，您将拥有多个单独的全局变量实例。另外，SWIG 不理解它，所以你真的别无选择......

工作示例：

test.h

enum VehicleSide 
    LEFT = 0,  ///< left side of vehicle is always 0
    RIGHT = 1  ///< right side of vehicle is always 1
;

/// Class to encode the ID of a vehicle wheel.
/// By convention, wheels are counted front to rear and left to right. In other
/// words, for a vehicle with 2 axles, the order is: front-left, front-right,
/// rear-left, rear-right.
class WheelID 
  public:
    WheelID(int id) : m_id(id), m_axle(id / 2), m_side(VehicleSide(id % 2)) 
    WheelID(int axle, VehicleSide side) : m_id(2 * axle + side), m_axle(axle), m_side(side) 

    /// Return the wheel ID.
    int id() const  return m_id; 

    /// Return the axle index for this wheel ID.
    /// Axles are counted from the front of the vehicle.
    int axle() const  return m_axle; 

    /// Return the side for this wheel ID.
    /// By convention, left is 0 and right is 1.
    VehicleSide side() const  return m_side; 

  private:
    int m_id;            ///< wheel ID
    int m_axle;          ///< axle index (counted from the front)
    VehicleSide m_side;  ///< vehicle side (LEFT: 0, RIGHT: 1)
;

// Instances of these global variables must be outside the header.
// What if the header was included in two files?
extern const WheelID FRONT_LEFT;
extern const WheelID FRONT_RIGHT;
extern const WheelID REAR_LEFT;
extern const WheelID REAR_RIGHT;

test.i

%module test

% // Section included verbatim in the generated wrapper source.

#include "test.h"

// One-time instances of the class.  In this case, directly
// added to the wrapper, but it could be in a separate .cpp file
// or .lib and linked to the final extension.
const WheelID FRONT_LEFT(0, LEFT);
const WheelID FRONT_RIGHT(0, RIGHT);
const WheelID REAR_LEFT(1, LEFT);
const WheelID REAR_RIGHT(1, RIGHT);

%

// Generate wrappers for test.h contents
%include "test.h"

演示：

>>> import test
>>> test.REAR_RIGHT.id()
3

【讨论】：

由于项目的许多部分都使用了这些 const，我决定按照您的建议在 .cpp 文件中定义它们。现在一切正常。非常感谢！

@UncleBen 不客气，欢迎来到 SO！如果这回答了您的问题，请考虑使用左侧的检查控件接受它。用upvotes表示感谢:^)