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我想定义结构指针的动态数组，我有 box2d 结构：

struct b2Vec2
{
    /// Default constructor does nothing (for performance).
    b2Vec2() {}

    /// Construct using coordinates.
    b2Vec2(float32 x, float32 y) : x(x), y(y) {}

    /// Set this vector to all zeros.
    void SetZero() { x = 0.0f; y = 0.0f; }

    /// Set this vector to some specified coordinates.
    void Set(float32 x_, float32 y_) { x = x_; y = y_; }

    /// Negate this vector.
    b2Vec2 operator -() const { b2Vec2 v; v.Set(-x, -y); return v; }

    /// Read from and indexed element.
    float32 operator () (int32 i) const
    {
        return (&x)[i];
    }

    /// Write to an indexed element.
    float32& operator () (int32 i)
    {
        return (&x)[i];
    }

    /// Add a vector to this vector.
    void operator += (const b2Vec2& v)
    {
        x += v.x; y += v.y;
    }

    /// Subtract a vector from this vector.
    void operator -= (const b2Vec2& v)
    {
        x -= v.x; y -= v.y;
    }

    /// Multiply this vector by a scalar.
    void operator *= (float32 a)
    {
        x *= a; y *= a;
    }

    /// Get the length of this vector (the norm).
    float32 Length() const
    {
        return b2Sqrt(x * x + y * y);
    }

    /// Get the length squared. For performance, use this instead of
    /// b2Vec2::Length (if possible).
    float32 LengthSquared() const
    {
        return x * x + y * y;
    }

    /// Convert this vector into a unit vector. Returns the length.
    float32 Normalize()
    {
        float32 length = Length();
        if (length < b2_epsilon)
        {
            return 0.0f;
        }
        float32 invLength = 1.0f / length;
        x *= invLength;
        y *= invLength;

        return length;
    }

    /// Does this vector contain finite coordinates?
    bool IsValid() const
    {
        return b2IsValid(x) && b2IsValid(y);
    }

    /// Get the skew vector such that dot(skew_vec, other) == cross(vec, other)
    b2Vec2 Skew() const
    {
        return b2Vec2(-y, x);
    }

    float32 x, y;
};

并且在 c++ 文件中，当我尝试使用新的 b2Vec2 结构设置数组时，我想定义 b2Vec2 的数组，我得到了错误：

error C2679: binary '=' : no operator found which takes a right-hand operand of type 'b2Vec2 *' (or there is no acceptable conversion)   


b2Vec2 *vertices = new b2Vec2[buffer.size()]; // its int number > 0
int verticeslength = polygon->buffer.size();
for (int ii=0, nn=verticeslength; ii<nn; ii++) {
    vertices[ii] = new b2Vec2(); // This is where the error .
}

我做错了什么？

4

2 回答 2

4

你错过了两个*：

b2Vec2 **vertices = new b2Vec2*[buffer.size()];
       ^                      ^

但是，最好使用std::vector而不是基本指针。

std::size_t N = buffer.size();

std::vector<std::vector<b2Vec2>> vertices (N, std::vector<b2Vec2>(N));
于 2013-11-10T20:48:33.737 回答
2

您也可以尝试根本不将它们分配为指针，并使用类似 std::vector 的东西来执行此操作：

#include <vector>

using namespace std;

...
{ 
   vector<b2Vec2> vertices;
   vertices.resize(buffer.size());

   // Use the vertices.
   for(int idx = 0; idx < vertices.size(); idx++)
   {  // Do something with each vertex
   }

}

我建议这样做的唯一原因是动态创建指针和数组通常会导致内存泄漏、睡眠丢失等。

如果您需要退货，可以退货。它也可以是封闭类的成员，由您的函数传入和初始化。您可以通过将其作为 vertices[idx] 访问来更改任何元素。你不必担心内存泄漏......你没有调用 new ，所以你不必调用 delete 。

于 2013-11-10T21:00:17.490 回答