Question

下面的代码使用八面体作为起始3D形状（我在网上找到它），经过一些调整后我仍然无法使其工作。

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stddef.h> /* must include for the offsetof macro */
#include <GL/glew.h>
#include <GL/glfw.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <stdlib.h>
#include <vector>
#include <iostream>

using namespace std; 

struct XYZ {
    GLdouble x;
    GLdouble y;
    GLdouble z;
};

struct FACET3 {
    XYZ p1;
    XYZ p2;
    XYZ p3;
};


void Normalise(XYZ *p_input)
{
    double magnitude = 0;
    magnitude = sqrt((p_input->x * p_input->x )+ (p_input->y * p_input->y) + (p_input->z * p_input->z));
    p_input->x = p_input->x / magnitude;
    p_input->y = p_input->y / magnitude;
    p_input->z = p_input->z / magnitude;

}

int CreateNSphere(FACET3 *f,int iterations)
{

   int i,it;
   double a;
   XYZ p[6] = {0,0,1,  0,0,-1,  -1,-1,0,  1,-1,0,  1,1,0, -1,1,0};
   XYZ pa,pb,pc;
   int nt = 0,ntold;

   /* Create the level 0 object */
   a = 1 / sqrt(2.0);
   for (i=0;i<6;i++) {
      p[i].x *= a;
      p[i].y *= a;
   }
   f[0].p1 = p[0]; f[0].p2 = p[3]; f[0].p3 = p[4];
   f[1].p1 = p[0]; f[1].p2 = p[4]; f[1].p3 = p[5];
   f[2].p1 = p[0]; f[2].p2 = p[5]; f[2].p3 = p[2];
   f[3].p1 = p[0]; f[3].p2 = p[2]; f[3].p3 = p[3];
   f[4].p1 = p[1]; f[4].p2 = p[4]; f[4].p3 = p[3];
   f[5].p1 = p[1]; f[5].p2 = p[5]; f[5].p3 = p[4];
   f[6].p1 = p[1]; f[6].p2 = p[2]; f[6].p3 = p[5];
   f[7].p1 = p[1]; f[7].p2 = p[3]; f[7].p3 = p[2];
   nt = 8;

   if (iterations < 1)
      return(nt);

   /* Bisect each edge and move to the surface of a unit sphere */
   for (it=0;it<iterations;it++) {
      ntold = nt;
      for (i=0;i<ntold;i++) {
         pa.x = (f[i].p1.x + f[i].p2.x) / 2;
         pa.y = (f[i].p1.y + f[i].p2.y) / 2;
         pa.z = (f[i].p1.z + f[i].p2.z) / 2;
         pb.x = (f[i].p2.x + f[i].p3.x) / 2;
         pb.y = (f[i].p2.y + f[i].p3.y) / 2;
         pb.z = (f[i].p2.z + f[i].p3.z) / 2;
         pc.x = (f[i].p3.x + f[i].p1.x) / 2;
         pc.y = (f[i].p3.y + f[i].p1.y) / 2;
         pc.z = (f[i].p3.z + f[i].p1.z) / 2;
         Normalise(&pa);
         Normalise(&pb);
         Normalise(&pc);
         f[nt].p1 = f[i].p1; f[nt].p2 = pa; f[nt].p3 = pc; nt++;
         f[nt].p1 = pa; f[nt].p2 = f[i].p2; f[nt].p3 = pb; nt++;
         f[nt].p1 = pb; f[nt].p2 = f[i].p3; f[nt].p3 = pc; nt++;
         f[i].p1 = pa;
         f[i].p2 = pb;
         f[i].p3 = pc;
      }
   }

   return(nt);
}


int main()
{
    FACET3 facet[8];
    int facets = CreateNSphere(facet, 2);
    printf(" Result: %d", facets);
}

当我尝试编译它时，它返回：

“细分错误”

gdb调试器说：

Program received signal SIGSEGV, Segmentation fault.
0x00000000004011df in CreateNSphere(FACET3*, int) ()

任何帮助？

用“-g”选项编译后，“gbd”返回了这个：

(gdb) run
Starting program: /home/alexander/Graphics/Code-Handouts/tut_3/a.out 

Program received signal SIGSEGV, Segmentation fault.
0x00000000004011df in CreateNSphere (f=0x7fffffffdeb0, iterations=2) at sphere_model.cpp:86
86           f[nt].p1 = pb; f[nt].p2 = f[i].p3; f[nt].p3 = pc; nt++;
(gdb) where
#0  0x00000000004011df in CreateNSphere (f=0x7fffffffdeb0, iterations=2) at sphere_model.cpp:86
#1  0x0000000000401303 in main () at sphere_model.cpp:100
(gdb)

Answer 1

对于两次迭代，您需要多于8个顶点。

初始迭代，有八个顶点。

在迭代1中，添加了24个。

在第二次迭代中，它再次翻两番。

所以你应该声明

FACET3 facet[128];

Answer 2

传递给CreateNSphere()的数组的大小为8.在CreateNSphere()内，您可以通过f索引变量访问您的nt数组，该变量在循环期间永久递增。所以基本上你有内存访问冲突 - 你尝试从它的大小访问f数组。当我对你的样本gdb进行调试时，显示当SIGSEGV收到时nt为48。

C ++在函数中传递数组指针地址

2 个答案: