C++中的訪問衝突錯誤

Question

我一直在嘗試解決程序中用於限制卷層次結構的訪問衝突。運行時出現訪問衝突錯誤。我已經使用了SDL和lib3d軟件包。

Error: Unhandled exception at 0x00fa2e80 in bvh.exe: 0xC0000005: Access violation reading location 0x00000004.

調用堆棧：>bvh.exe!Triangle::Triangle(const Vertex * vertexA, const Vertex * vertexB, const Vertex * vertexC, unsigned int r, unsigned int g, unsigned int b, bool twosided, bool triNormalProvided, Float3 triNormal)線393 +量0x150字節C++

我在下面的方式定義我的結構：

struct Float3 
{ 
    float X, Y Z; 
    Float3(float x=0, float y=0, float z=0) 
     : 
    X(x), Y(y), Z(z){} 

    Float3(const Float3& rhs) 
     : 
    X(rhs.X), Y(rhs.Y), Z(rhs.Z){} 

    inline Float3& operator+=(const Float3& rhs) 
    { 
    X += rhs.X; Y += rhs.Y; Z += rhs.Z; return *this; 
    } 

    // similar for the other operators 

    void assignSmaller(const Float3& rhs) 
    { 
     X = min(X, rhs.X); 
     Y = min(Y, rhs.Y); 
     Z = min(Z, rhs.Z); 
    } 

    void assignBigger(const Float3& rhs) 
     { 
     X = max(X, rhs.X); 
     Y = max(Y, rhs.Y); 
     Z = max(Z, rhs.Z); 
     } 

    float length() 
    { 
    return sqrt(X*X +Y*Y + Z*Z); 
    } 

    inline float lengthsq() 
    { 
    return X*X +Y*Y + Z*Z; 
    } 

    inline void Normalize() 
    { 
    float norm = length(); 
    X/= norm; Y/= norm; Z/= norm; 
    } 
}; 

struct Vertex : public Float3 
{ 
    Float3 n; 
    unsigned _ambientOcclusionCoeff; 

    Vertex(float x, float y, float z, float nx, float ny, float nz, unsigned char amb=60) 
    : 
    Float3(x,y,z), n(nx,ny,nz), _ambientOcclusionCoeff(amb){} 

}; 

struct Pixel { 
    float _b, _g, _r; 
    Pixel(float r=0.f, float g=0.f, float b=0.f) 
    : 
    _b(b), _g(g), _r(r) {} 

Pixel& operator+=(const Pixel& rhs) { _b += rhs._b; _g += rhs._g; _r += rhs._r; return *this; } 
    // similar for the other operators 

}; 

struct Triangle 
{ 
    const Vertex *_vertexA, *_vertexB, *_vertexC; 
    Float3 centroid, n; 
    // Color: 
    Pixel _colorf; 
    // precomputed for SDL surface 
    Uint32 _color; 

    // Should we backface cull this triangle? 
    bool _twoSided; 

    // Raytracing intersection pre-computed cache: 
    float _d, _d1, _d2, _d3; 
    Float3 _e1, _e2, _e3, _bottom, _top; 

    Triangle(
    const Vertex *vertexA, 
     const Vertex *vertexB, 
    const Vertex *vertexC, 
    unsigned r, unsigned g, unsigned b, 
    bool twosided = false, bool triNormalProvided=false, 
    Float3 triNormal=Float3(0.0f,0.0f,0.0f)) 
    : 

    _vertexA(vertexA), _vertexB(vertexB), _vertexC(vertexC), 

    centroid((vertexA->X + vertexB->X + vertexC->X)/3.0f, 
     (vertexA->Y + vertexB->Y + vertexC->Y)/3.0f, 
     (vertexA->Z + vertexB->Z + vertexC->Z)/3.0f), 

    _colorf((float)r,(float)g,(float)b), // For use in all other cases 
    _color(SDL_MapRGB(Screen::_surface->format, r,g,b)), // For use with DrawPixel 

    _twoSided(twosided), 

    _bottom(FLT_MAX,FLT_MAX, FLT_MAX), // Will be updated after centering in Loader 
    _top(-FLT_MAX, -FLT_MAX,-FLT_MAX) // Will be updated after centering in Loader 
    { 
     // this is where the debugger points to with an access violation error. 
     if (!triNormalProvided) 
     { 
     n = Float3((vertexA->n.X + vertexB->n.X + vertexC->n.X)/3.0f, 
       (vertexA->n.Y + vertexB->n.Y + vertexC->n.Y)/3.0f, 
       (vertexA->n.Z + vertexB->n.Z + vertexC->n.Z)/3.0f); 
     n.Normalize(); 
     } 
     else {n = triNormal;} 
     } 
}; 

Answer 1

你不 「避免訪問衝突錯誤」 通過更改IDE中的設置。

您通過修復代碼來解決這些故障。您在某處破壞內存，解除引用無效指針，在緩衝區末尾寫入/讀取，free已釋放的內存......

Answer 2

看起來您試圖訪問第二個成員變量該成員函數中的三角形，而指針this爲NULL。

或者，也許一旦傳入的頂點指針爲NULL。

舉個例子，這將產生你所看到的錯誤：

struct Foo 
{ 
    void bar() { cout << b << end; } 
    int a, b; 
}; 

int main() 
{ 
    Foo* f = 0; 
    f->bar(); 
    return 0; 
} 

到b訪問在bar()會實際上是一個int訪問由4（sizeof(int)）偏移this。如果this是NULL（如示例中所示），那麼您將在位置0x00000004處發生訪問衝突。

確保所有的指針都是有效的。

Answer 3

我嚴重懷疑0x00000004指向的東西。通常這樣的數字不會;他們太「正常」了。你不能取消引用int。