访问存储在矢量中的指针的值

我正在尝试创建一个三角形网格来编写有限元分析的代码。我知道已经编写了软件来做到这一点，但这是为类项目准备的。

我正在尝试做的是将该区域划分为均匀分布的节点(网格点)。每个节点都有 6 个三角形连接到它，需要在计算中使用。为了方便起见，我创建了两个结构，一个用于节点，一个用于三角形。

下面，我有一个我试图在我的代码中实现的内容的最小工作示例。但是，此代码在将 x，y 值分配给顶点的行上收到分段错误。在 gdb 中生成的错误指出：

With using vectors (as per the minimum working example)
----------------------------
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400f90 in std::vector<Node*, std::allocator<Node*> >::operator[] (this=0x0, __n=0)
at /usr/include/c++/4.8/bits/stl_vector.h:771
771           { return *(this->_M_impl._M_start + __n); }
// Running backtrace
(gdb) bt
#0  0x0000000000400f90 in std::vector<Node*, std::allocator<Node*> >::operator[] (this=0x0, __n=0)
at /usr/include/c++/4.8/bits/stl_vector.h:771
#1  0x0000000000400a87 in main () at minimumexample.cpp:28
----------------------------

我不知道如何弄清楚这一点。如果我使用数组代替向量，则会产生类似的错误，所以我认为这只是向量类的问题吗？

With arrays instead of vectors
----------------------------
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400929 in main () at minimumexample.cpp:28
28        MyGrid[0].Triangles[0]->vertex[0]->x = 0;
// Running backtrace
(gdb) bt
#0  0x0000000000400929 in main () at minimumexample.cpp:28
----------------------------

下面是我正在尝试做的事情的最小工作示例。我不确定为什么我会收到越界错误，因为我根本没有看到我在向量中越界的位置。

#include <iostream>
#include <vector>
using namespace std;
struct Triangle;
struct Node
{
double x; 
double y;
vector<Triangle*> Triangles;  
Node() : Triangles(6) {}
};
struct Triangle
{
vector<Node*> vertex;
Triangle() : vertex(3) {} // 3 vertices per triangle
};
int main()
{
int size = 10;
vector<Node> MyGrid(size);
double spacing = .25;
// The below code should create 3 vertices of the triangle with the
// three vertices of the triangle (x,y) defined as locations (0,0) for the 
// first vertex, (1,0) for the second vertex, and (1,1) for the third.
MyGrid[0].Triangles[0]->vertex[0]->x = 0; // Line 28: Error here
MyGrid[0].Triangles[0]->vertex[0]->y = 0;
MyGrid[0].Triangles[0]->vertex[1]->x = 1;
MyGrid[0].Triangles[0]->vertex[1]->y = 0;
MyGrid[0].Triangles[0]->vertex[2]->x = 1;
MyGrid[0].Triangles[0]->vertex[2]->y = 1;
return 0;
}

对于遇到此问题的任何其他人，这是代码的工作版本：

#include <iostream>
#include <vector>
using namespace std;
struct Triangle;
struct Node
{
double x; 
double y;
Triangle *Triangles;  
};
struct Triangle
{
Node *vertex;
};
int main()
{
int size = 10;
vector<Node> MyGrid(size);
double spacing = .25;
// Allocate 6 Triangle objects into the variable Triangles
MyGrid[0].Triangles = new Triangle[6];
// Allocate 3 nodes for Triangles[0]'s vertex
MyGrid[0].Triangles[0].vertex = new Node[3];
MyGrid[0].Triangles[0].vertex[0].x = 0; 
MyGrid[0].Triangles[0].vertex[0].y = 0;
MyGrid[0].Triangles[0].vertex[1].x = 1;
MyGrid[0].Triangles[0].vertex[1].y = 0;
MyGrid[0].Triangles[0].vertex[2].x = 1;
MyGrid[0].Triangles[0].vertex[2].y = 1;
return 0;
}