Question

我是C的新手，目前在C中进行BREP（边界表示）实现，其思路是：给定拓扑矩阵和顶点矩阵，以生成具有实体连通性信息的有序表。我遇到的问题是这两个循环：

主循环

 while(next < n_triang)
{
    /* extract the triangle to be used and the next in queue */
    next = extract_next(grid_triang, n_triang, next, &current_triang);

    /* set triang_vertex as the current triangle */
    for(i = 0; i < VERTEX_COUNT; i++)
    {
        triang_vertex[i] = (int)grid_triang[current_triang][i];
    }

    /* find the orientation of the current triangle */
    orientation_wrong = find_connection(triang_vertex, grid_edges, &n_edges, &partner_triang, &partner_edge);

    /* if there is no partner triangle, set status to free */
    if(partner_triang == FALSE)
    {
        grid_triang[current_triang][USE_INDEX] = TRIANG_FREE;
    }
    else
    {
        /* if orientation is wrong, change the order of vertex and add the triangle to the mesh */
        if( orientation_wrong == TRUE)
        {
            temp = triang_vertex[Y_];
            triang_vertex[Y_] = triang_vertex[Z_];
            triang_vertex[Z_] = temp;

            for(i=0; i<VERTEX_COUNT; i++)
            {
                grid_triang[current_triang][i] = (float)triang_vertex[i];
            }

            add_triangle(triang_vertex, next, grid_vertex, grid_edges, &current_triang, &n_edges);

            /* add the current triangle to the faces grid */
            for (i = 0; i < n_points; i++)
            {
                grid_faces[i][current_triang] = triang_vertex[i];
            }           
        }
        else
        {
            /* if orientation is correct, add the triangle to the mesh and to the faces grid */
            add_triangle(triang_vertex, next, grid_vertex, grid_edges, &current_triang, &n_edges);

            for (i = 0; i < VERTEX_COUNT; i++)
            {
                grid_faces[i][current_triang] = triang_vertex[i];
            }
        }
    }
}

extract_next功能

 int extract_next(float **grid_triang, int n_triang, int next, int *current_triang)
{
/* define variables */
int new_next = 0, visited_triang = 0, kill = 0;
int found_triang = FALSE;

/* if triangle is used throw error */
if(grid_triang[next][USE_INDEX] == TRIANG_USED )
{
    perror("Current triangle not available");
    exit(EXIT_FAILURE);
}
else *current_triang = next; /* set current triangle to output */

/* change status to used */
grid_triang[next][USE_INDEX] = TRIANG_USED;
next++;

/* start the iteration */
while(!found_triang && visited_triang < n_triang)
{
        /* if triangle is used, go to next triangle and add a visited */
    if(grid_triang[next][USE_INDEX] == TRIANG_USED)
    {
        next++;
        visited_triang++;
        printf("Used, moving");
    }
    else if(grid_triang[next][USE_INDEX] == TRIANG_FREE)
    {
            /* if triangle is free then break the loop */
        found_triang = TRUE;
        printf("found a free one!\n");
    }
    else printf("not valid");

}

/* if found triangle set the next triangle to output */
if (found_triang)
{
    new_next = next;
}

printf("New triangle extracted\n");
return new_next;

}

当变量 next 等于 n_triang 时，代码应停止执行，但代码会无限期地执行，我无法理解原因（即使是逐步调试）。这是输出：

正如您所看到的，当它达到 n_triang 的值时，它应该停止但是会无限期地继续。

感谢任何可以提供帮助的人。

Answer 1

我怀疑你的问题在于：

/* start the iteration */
while(!found_triang && visited_triang < n_triang)
{
        /* if triangle is used, go to next triangle and add a visited */
    if(grid_triang[next][USE_INDEX] == TRIANG_USED)
    {
        next++;
        visited_triang++;
        printf("Used, moving");
    }
    else if(grid_triang[next][USE_INDEX] == TRIANG_FREE)
    {
            /* if triangle is free then break the loop */
        found_triang = TRUE;
        printf("found a free one!\n");
    }
    else printf("not valid");

}

/* if found triangle set the next triangle to output */
if (found_triang)
{
    new_next = next;
}

printf("New triangle extracted\n");
return new_next;

您正在测试是否使用了三角形，这表明您认为三角形是某种内存池。＆＃34;这很好。

但是，您不会将索引变量（next）限制为保持在池的范围内。我相信你会得到一个相当高的起点，然后走出阵列的末端。

我建议您添加一些索引检查，并在需要时将索引包装回零：

#define TRIANGLE_USED(n) (grid_triang[(n)][USE_INDEX] == TRIANG_USED)

for (n_visited = 0; n_visited < n_triang; ++n_visited)
{
    // The `next` variable is an index into a pool of triangles.
    // Don't overrun the pool - reset to the bottom if needed.
    if (next >= n_triang) {
        next = 0;
    }

    if (TRIANGLE_USED(next)) {
        printf("Triangle %d is used. Skipping.", next);          
        ++next;
    }        
    else {
        printf("Triangle %d is free. Stopping.", next);
        break;
    }
    /*NOTREACHED*/
}

return next;

代码中的无限循环

1 个答案: