C ++变量数据被覆盖

时间：2009-08-05 13:45:50

标签： c++ vector pointers overwrite

自从我编写C / C ++以来已经过了几年，现在我遇到了一个我自己似乎无法解决的问题。

给出以下结构：

struct InputData
{
    float diameter;
    float length;
    int vertIndex;
    struct InputData *parent;
    vector<InputData*> children;
    bool deadEnd;

    InputData(float dia, float lngth)
    {
        diameter = dia;
        length = lngth;
        vertIndex = NULL;
        parent = NULL;
        deadEnd = false;
    }
};

我首先定义了许多节点及其父/子关系：

InputData i0 = InputData(3.0f, 3.0f);
InputData i1 = InputData(2.0f, 2.0f);
InputData i2 = InputData(1.0f, 1.0f);
InputData i3 = InputData(1.0f, 1.0f);
InputData i4 = InputData(1.0f, 1.0f);
InputData i5 = InputData(1.01f, 0.5f);

i0.children.push_back(&i1);
i1.children.push_back(&i2);
i2.children.push_back(&i3);
i3.children.push_back(&i4);
i4.children.push_back(&i5);

i1.parent = &i0;
i2.parent = &i1;
i3.parent = &i2;
i4.parent = &i3;
i5.parent = &i4;

请注意，i5作为唯一节点没有任何子节点。

然后我继续使用这些数据做一些工作（从main（）调用BuildMeshVertices（＆amp; i0，＆amp; vertices），最后将一个子项添加到i5：

void BuildMeshVertices(InputData* current, vector<SimpleVertex> *vertices)
{
    //Do work

    if(current->children.size() == 1)
    {
        BuildMeshVertices(current->children[0], vertices);
    }
    else if(current->children.size() == 0 && current->deadEnd == false)
    {
        InputData iDeadEnd = InputData(1.01f, 0.5f);
        iDeadEnd.deadEnd = true;
        iDeadEnd.parent = current;
        current->children.push_back(&iDeadEnd);     

        BuildMeshVertices(&iDeadEnd, vertices);
    }
}

之后一切都很好。 i0有一个孩子（i1），i1有一个孩子（i2），依此类推，i5现在也有一个孩子。

我调用了另一个函数（BuildMeshIndices（）），突然在这个函数（第63行）中输入几行，新添加的子节点到i5的数据被覆盖。 i5仍指向正确的孩子，但这个孩子的数据突然出现乱码。

这是截图before and after（对于链接感到抱歉，但我不允许使用IMG标签）

我无法弄清楚为什么会发生这种情况，但我觉得这与我糟糕的内存管理有关？

UPDATE 此外，不必这样做。例如，如果将子矢量更改为值向量是首选的C ++方式，我宁愿这样做。我试图评论答案，但我不确定你们是否看到了评论（根据常见问题解答，您需要50点声明才能发表评论）？

以下是完整的源代码（一切都没有被删除，但足以重现错误）：

#include "stdafx.h"
#include <vector>

using std::vector;

struct InputData
{
    float diameter;
    float length;
    int vertIndex;
    struct InputData *parent;
    vector<InputData*> children;
    bool deadEnd;

    InputData(float dia, float lngth)
    {
        diameter = dia;
        length = lngth;
        vertIndex = NULL;
        parent = NULL;
        deadEnd = false;
    }
};

//--------------------------------------------------------------------------------------
// Vertex types
//--------------------------------------------------------------------------------------
struct SimpleVertex
{
    float Pos;

    SimpleVertex(float Position)
    {
        Pos = Position;
    }
};

void BuildMeshVertices(InputData* current, vector<SimpleVertex> *vertices)
{
    current->vertIndex = vertices->size();

    //Add vertices..

    if(current->children.size() == 1)
    {
        BuildMeshVertices(current->children[0], vertices);
    }
    else if(current->children.size() == 0 && current->deadEnd == false)
    {
        InputData iDeadEnd = InputData(1.01f, 0.5f);
        iDeadEnd.deadEnd = true;
        iDeadEnd.parent = current;
        current->children.push_back(&iDeadEnd);     

        BuildMeshVertices(&iDeadEnd, vertices);
    }
}

void BuildMeshIndices(InputData* current, vector<unsigned long> *indices)
{
    indices->push_back(current->vertIndex+2);
    indices->push_back(current->vertIndex+0);
    indices->push_back(current->vertIndex+1);
    indices->push_back(current->vertIndex+3);
    indices->push_back(current->vertIndex+0);
    indices->push_back(current->vertIndex+2);

    InputData *parent = current->parent;

    unsigned long vOffset;

    if(parent != NULL && parent->children.size() == 1)
    {   
        vOffset = (unsigned long)current->vertIndex;

        indices->push_back(vOffset+7);
        indices->push_back(vOffset+5);
        indices->push_back(vOffset+4);
        indices->push_back(vOffset+6);
        indices->push_back(vOffset+5);
        indices->push_back(vOffset+7);

        indices->push_back(vOffset+10);
        indices->push_back(vOffset+8);
        indices->push_back(vOffset+9);
        indices->push_back(vOffset+11);
        indices->push_back(vOffset+8);
        indices->push_back(vOffset+10);

        indices->push_back(vOffset+15);
        indices->push_back(vOffset+13);
        indices->push_back(vOffset+12);
        indices->push_back(vOffset+14);
        indices->push_back(vOffset+13);
        indices->push_back(vOffset+15);

        indices->push_back(vOffset+18);
        indices->push_back(vOffset+16);
        indices->push_back(vOffset+17);
        indices->push_back(vOffset+19);
        indices->push_back(vOffset+16);
        indices->push_back(vOffset+18);
    }

    if(current->children.size() == 1 && current->deadEnd == false)
    {
        BuildMeshIndices(current->children[0], indices);
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    InputData i0 = InputData(3.0f, 3.0f);
    InputData i1 = InputData(2.0f, 2.0f);
    InputData i2 = InputData(1.0f, 1.0f);
    InputData i3 = InputData(1.0f, 1.0f);
    InputData i4 = InputData(1.0f, 1.0f);
    InputData i5 = InputData(1.01f, 0.5f);

    i0.children.push_back(&i1);
    i1.children.push_back(&i2);
    i2.children.push_back(&i3);
    i3.children.push_back(&i4);
    i4.children.push_back(&i5);

    i1.parent = &i0;
    i2.parent = &i1;
    i3.parent = &i2;
    i4.parent = &i3;
    i5.parent = &i4;

    // Create vertex buffer
    vector<SimpleVertex> vertices;

    BuildMeshVertices(&i0, &vertices);

    // Create index buffer
    vector<unsigned long> indices;

    BuildMeshIndices(&i0, &indices);

    return 0;
}

5 个答案:

答案 0 :(得分：7)

您正在将指向堆栈对象的指针推入向量中。一旦执行离开范围，堆栈对象将被销毁并且内存将被重用，从而导致伪造值。尝试

InputData *iDeadEnd = new InputData(1.01f, 0.5f);
iDeadEnd->deadEnd = true;
iDeadEnd->parent = current;
current->children.push_back(iDeadEnd);

然后你必须在适当的时候释放那段记忆。

答案 1 :(得分：1)

您应该使用动态内存来处理指针。当您退出 BuildMeshVertices 函数时， InputData 将被销毁，因此数据将被吞噬或您将获得内存异常。

您应该执行类似

的操作 
InputData * iDeadEnd = new InputData(1.01f, 0.5f);

而不是

InputData iDeadEnd = InputData(1.01f, 0.5f);

答案 2 :(得分：1)

您正在STACK上实例化iDeadEnd，并获取指向堆栈地址的指针！当函数终止并且堆栈展开时，iDeadEnd的数据将变为乱码。

InputData *iDeadEnd = new InputData(1.01f, 0.5f);
iDeadEnd->deadEnd = true;
iDeadEnd->parent = current;
current->children.push_back(iDeadEnd);         

BuildMeshVertices(iDeadEnd, vertices);

您现在遇到的问题是，当您完成iDeadEnd时，需要显式释放内存。

答案 3 :(得分：1)

将原始指针更改为smart pointers，您将遇到内存管理问题。

您无需将所有提升复制到项目中，只需要复制所需的标题。

#include <vector>
#include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>

struct InputData
{
    float diameter;
    float length;
    unsigned long vertIndex;
    boost::weak_ptr<InputData> parent;
    std::vector< boost::shared_ptr<InputData> > children;
    bool deadEnd;

    InputData(float dia, float lngth, boost::weak_ptr<InputData> p = boost::weak_ptr<InputData>(), bool de = false)
        : diameter(dia), length(lngth), vertIndex(0), parent(p), deadEnd(de) {}
};

struct SimpleVertex
{
    float Pos;

    SimpleVertex(float position) : Pos(position) {}
};

void BuildMeshVertices(boost::shared_ptr<InputData> current, std::vector<SimpleVertex>& vertices)
{
    current->vertIndex = vertices.size();

    //Add vertices..
    if(current->children.size() == 1)
    {
        BuildMeshVertices(current->children[0], vertices);
    }
    else if(current->children.size() == 0 && current->deadEnd == false)
    {
          // this was a stack variable, so the pointer became invalid when going out of ambit.
        boost::shared_ptr<InputData> iDeadEnd( new InputData(1.01f, 0.5f, current, true) );
        current->children.push_back(iDeadEnd);         

        BuildMeshVertices(iDeadEnd, vertices);
    }
}

void BuildMeshIndices(boost::shared_ptr<InputData> current, std::vector<unsigned long>& indices)
{
    unsigned long vi = current->vertIndex;
    unsigned long  ioffset[] = { vi+2, vi, vi+1, vi+3, vi, vi+2};
    indices.insert(indices.end(), ioffset, ioffset+6);

    boost::shared_ptr<InputData> parent = current->parent.lock();
    if (parent && parent->children.size() == 1)
    {   
        unsigned long offs = current->vertIndex;
          unsigned long voffset[] = 
          { offs+7, offs+5, offs+4, offs+6, offs+5, offs+7,
            offs+10, offs+8, offs+9, offs+11, offs+8, offs+10,
            offs+15, offs+13, offs+12, offs+14, offs+13, offs+15,
            offs+18, offs+16, offs+17, offs+19, offs+16, offs+18 };
          indices.insert(indices.end(), voffset, voffset+24);
    }

    if(current->children.size() == 1 && current->deadEnd == false)
    {
        BuildMeshIndices(current->children[0], indices);
    }
}

int main()
{
    boost::shared_ptr<InputData> i0( new InputData(3.0f, 3.0f) );
    boost::shared_ptr<InputData> i1( new InputData(2.0f, 2.0f) );
    boost::shared_ptr<InputData> i2( new InputData(1.0f, 1.0f) );
    boost::shared_ptr<InputData> i3( new InputData(1.0f, 1.0f) );
    boost::shared_ptr<InputData> i4( new InputData(1.0f, 1.0f) );
    boost::shared_ptr<InputData> i5( new InputData(1.01f, 0.5f) );

    i0->children.push_back(i1);
    i1->children.push_back(i2);
    i2->children.push_back(i3);
    i3->children.push_back(i4);
    i4->children.push_back(i5);

    i1->parent = i0;
    i2->parent = i1;
    i3->parent = i2;
    i4->parent = i3;
    i5->parent = i4;

    // Create vertex buffer
    std::vector<SimpleVertex> vertices;
    BuildMeshVertices(i0, vertices);

    // Create index buffer
    std::vector<unsigned long> indices;
    BuildMeshIndices(i0, indices);

    return 0;
}

认为你还有一半的半C ++脏代码......你应该选择一种语言。

答案 4 :(得分：0)

当您的BuildMeshVertices函数退出时，iDeadEnd（i5的子）被解构，因为您在堆栈上声明它并退出函数，整个堆栈帧无效并且所有对象都被解构。您要么动态分配iDeadEnd，要么从根本上重新思考如何定义树。你最好让每个结构保存一个InputData（而不是InputData *）的向量，然后按如下方式设置它们：

InputData i0 = InputData(3.0f, 3.0f);
i0.children.push_back( InputData( 2.0f, 2.0f ) );
i0.children[0].children.push_back( InputData( 1.0f, 1.0f ) );

等

由于显而易见的原因，即使这远非理想。定义一个元素树绝不是最有趣的事情。

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