C++ 结构指针数组

Question

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;
};

在c++文件中我想定义b2Vec2的数组当我尝试使用新的 b2Vec2 结构设置数组时出现错误:

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？

Answer 1

你错过了两个*:

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

但是，最好使用 std::vector 而不是 basre 指针。

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

std::vector<std::vector<b2Vec2>> vertices (N, std::vector<b2Vec2>(N));