java - BOX2D - 将 NULL 常量隐式转换为 'bool' [-Wnull-conversion]

Question

我正在尝试使用 android ndk 将 Box2D 编译为适用于 android 的 64 位版本

但是我遇到了很多这样的错误:

andEnginePhysicsBox2DExtension/src/main/jni\Box2D/Collision/Shapes/b2ChainShape.h:111:20: warning: implicit conversion of NULL constant to 'bool' [-Wnull-conversion] m_hasPrevVertex = NULL; ~ ^~~~ false

这就是我的 b2ChainShape.h 的内容

/*
* Copyright (c) 2006-2010 Erin Catto http://www.box2d.org
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

#ifndef B2_CHAIN_SHAPE_H
#define B2_CHAIN_SHAPE_H

#include <Box2D/Collision/Shapes/b2Shape.h>

class b2EdgeShape;

/// A chain shape is a free form sequence of line segments.
/// The chain has two-sided collision, so you can use inside and outside collision.
/// Therefore, you may use any winding order.
/// Since there may be many vertices, they are allocated using b2Alloc.
/// Connectivity information is used to create smooth collisions.
/// WARNING: The chain will not collide properly if there are self-intersections.
class b2ChainShape : public b2Shape
{
public:
    b2ChainShape();

    /// The destructor frees the vertices using b2Free.
    ~b2ChainShape();

    /// Create a loop. This automatically adjusts connectivity.
    /// @param vertices an array of vertices, these are copied
    /// @param count the vertex count
    void CreateLoop(const b2Vec2* vertices, int32 count);

    /// Create a chain with isolated end vertices.
    /// @param vertices an array of vertices, these are copied
    /// @param count the vertex count
    void CreateChain(const b2Vec2* vertices, int32 count);

    /// Establish connectivity to a vertex that precedes the first vertex.
    /// Don't call this for loops.
    void SetPrevVertex(const b2Vec2& prevVertex);

    /// Establish connectivity to a vertex that follows the last vertex.
    /// Don't call this for loops.
    void SetNextVertex(const b2Vec2& nextVertex);

    /// Implement b2Shape. Vertices are cloned using b2Alloc.
    b2Shape* Clone(b2BlockAllocator* allocator) const;

    /// @see b2Shape::GetChildCount
    int32 GetChildCount() const;

    /// Get a child edge.
    void GetChildEdge(b2EdgeShape* edge, int32 index) const;

    /// This always return false.
    /// @see b2Shape::TestPoint
    bool TestPoint(const b2Transform& transform, const b2Vec2& p) const;

    /// Implement b2Shape.
    bool RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
                    const b2Transform& transform, int32 childIndex) const;

    /// @see b2Shape::ComputeAABB
    void ComputeAABB(b2AABB* aabb, const b2Transform& transform, int32 childIndex) const;

    /// Chains have zero mass.
    /// @see b2Shape::ComputeMass
    void ComputeMass(b2MassData* massData, float32 density) const;

    /// Get the number of vertices.
    int32 GetVertexCount() const { return m_count; }

    /// Get the vertices (read-only).
    const b2Vec2& GetVertex(int32 index) const
    {
        b2Assert(0 <= index && index < m_count);
        return m_vertices[index];
    }

    /// Get the vertices (read-only).
    const b2Vec2* GetVertices() const { return m_vertices; }

    /// The vertices. Owned by this class.
    b2Vec2* m_vertices;

    /// The vertex count.
    int32 m_count;

    b2Vec2 m_prevVertex, m_nextVertex;
    bool m_hasPrevVertex, m_hasNextVertex;
};

inline b2ChainShape::b2ChainShape()
{
    m_type = e_chain;
    m_radius = b2_polygonRadius;
    m_vertices = NULL;
    m_count = 0;
    m_hasPrevVertex = NULL;
    m_hasNextVertex = NULL;
}

#endif

如有任何建议，我们将不胜感激

Answer 1

你在这里得到的警告

implicit conversion of NULL constant to 'bool' [-Wnull-conversion] m_hasPrevVertex = NULL; ~ ^~~~ false

告诉您，您有 bool 字段，这些字段是用 NULL 而不是实际的 boolean 值初始化的。例如 m_hasPrevVertex 和 m_hasNextVertex。因此，编译器试图通过将这些值隐式设置为 false 并通知您这一事实来解决此问题。

在这种情况下，这不是严重错误，但绝对是代码味道。 (虽然，也许不同的编译器实际上会在这里抛出错误，我不确定)

您可以通过简单地将所有 boolean 值初始化为 true 或 false 来消除这些警告，具体取决于您的用例。