【发布时间】：2016-04-21 10:16:29
【问题描述】：
在使用 gdb 或将许多 printfs 放入以下代码之后，我都无法找到分段错误错误发生的位置：
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "../GCGraLib2/GCGraLib2.h"
#define DIM 100
这里我们计算一个点和数组中的一组点之间的距离
float *dist2(int px,int py,int x[],int y[])
{
float min,d;int i=1;min=pow(abs(px-x[0]),2)+pow(abs(py-y[0]),2);;
int nearestp;static float output[2];
while (i<=DIM) {
d=pow(abs(px-x[i]),2)+pow(abs(py-y[i]),2);
if (d<min){min=d;}
i++;
}
nearestp=i-1;
output[0]=d;output[1]=nearestp;
return output;
}
这里是下面描述的多边形的重绘
void redraw(int n, int x[], int y[],SDL_Renderer *ren)
{
int i;
GC_FillCircle(ren,x[0],y[0],3);
for (i=1; i<=n; i++)
{
SDL_RenderDrawLine(ren, x[i-1], y[i-1], x[i], y[i]);
GC_FillCircle(ren,x[i],y[i],3);
}
}
对事件队列使用过滤器
int isMouseEvent(int * motioncounter,SDL_Event * event) {
*motioncounter=*motioncounter+1;
if (*motioncounter<=5) {
return 0;}
else {
*motioncounter=0;
return 1;
}
}
这是用贝塞尔曲线对一组点进行插值
void bezier(SDL_Renderer *ren, int x[], int y[], int n)
{
int i,k,tempo,indice;
float t = 0;
float xx[DIM],yy[DIM];
float bx[DIM],by[DIM];
printf("BEZIER\n");
// coefficienti da usare nell'algoritmo
for (tempo=0;tempo<=99;tempo++)
{
for (indice=0;indice<=n;indice++)
{
xx[indice]=x[indice];
}
for (indice=0;indice<=n;indice++)
{
yy[indice]=y[indice];
}
for (k=1;k<n;k++)
{
for (i=0;i<n-k;i++)
{
// trovo coordinante della curva al tempo t
xx[i]=(1-t)*xx[i]+t*xx[i+1];
yy[i]=(1-t)*yy[i]+t*yy[i+1];
}
}
//coordinate del punto
bx[tempo]=xx[0];
by[tempo]=yy[0];
t=t+0.01;
}
// aggiornare ren con coordinate curva
// rendo tutto le schermo nero
SDL_SetRenderDrawColor(ren, 0, 0, 0, 255);
SDL_RenderClear(ren);
// ristampare i punti
for (i=0;i<n;i++)
{
SDL_SetRenderDrawColor(ren, 255, 255, 0, 255);
GC_FillCircle(ren,x[i],y[i],3);
}
for (tempo=0;tempo<=98;tempo++)
{
SDL_RenderDrawLine(ren, bx[tempo], by[tempo], bx[tempo+1], by[tempo+1]);
}
}
这里我们控制I/O的通量
int main(void)
{
SDL_Window *win;
SDL_Renderer *ren;
SDL_Event event;
int vxmax,vymax;
int esc=1,i,j,n=0;SDL_EventFilter prune=0;
int x[DIM],y[DIM];int readytomove=0;
float *DIST;float dist;int nearestp;
Uint32 windowID;int motioncounter=0;
if(SDL_Init(SDL_INIT_VIDEO)<0)
{
fprintf(stderr,"Couldn't init video: %s\n",SDL_GetError());
return(1);
}
vxmax=300;
vymax=300;
win= SDL_CreateWindow("Inter_Polygon", 100, 100, vxmax, vymax,
SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE);
if(win==NULL){
fprintf(stderr,"SDL_CreateWindow Error: %s\n",SDL_GetError());
SDL_Quit();
return 1;
}
ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
if (ren == NULL){
SDL_DestroyWindow(win);
fprintf(stderr,"SDL_CreateRenderer Error: %s\n",SDL_GetError());
SDL_Quit();
return 1;
}
SDL_SetRenderDrawColor(ren, 0, 0, 0, 255);
SDL_RenderClear(ren);
SDL_SetRenderDrawColor(ren, 255, 0, 50, 255);
SDL_RenderPresent(ren);
这里我们通过点击一些点来绘制一个多边形。要退出，请按 Esc 键。
while(esc)
{
if (SDL_PollEvent(&event))
prune=(SDL_EventFilter) isMouseEvent(& motioncounter,&event);
SDL_SetEventFilter(prune,& motioncounter);
switch(event.type)
{
case SDL_MOUSEBUTTONDOWN:
if(event.button.button==1)
{
DIST = dist2(event.button.x,event.button.y,x,y);nearestp=DIST[1];dist=DIST[0];
if (dist >= 6.5) {
readytomove=0;
x[n]=event.button.x;
y[n]=event.button.y;
GC_FillCircle(ren,x[n],y[n],3);
if(n>1) {
printf("CALL TO BEZIER: n=%i\n",n);
// SDL_RenderDrawLine(ren, x[n-1], y[n-1], x[n], y[n]);
bezier(ren,x,y,n);
n++;
}
else{readytomove=1;}
}
}
break;
case SDL_MOUSEMOTION:
if(event.button.button==1)
{
DIST = dist2(event.button.x,event.button.y,x,y);nearestp=DIST[1];dist=DIST[0];
if (readytomove)
{
x[nearestp]=event.button.x;
y[nearestp]=event.button.y;
GC_FillCircle(ren,x[1],y[1],3);
if(n>0){
bezier(ren,x,y,n);
n++;
}
}
}
SDL_RenderPresent(ren);
break;
case SDL_KEYDOWN:
if(event.key.keysym.sym == SDLK_ESCAPE)
esc=0;
break;
case SDL_WINDOWEVENT:
windowID = SDL_GetWindowID(win);
if (event.window.windowID == windowID) {
switch (event.window.event) {
case SDL_WINDOWEVENT_SIZE_CHANGED: {
vxmax = event.window.data1;
vymax = event.window.data2;
// printf("vxmax= %d \n vymax= %d \n", vxmax,vymax);
SDL_SetRenderDrawColor(ren, 0, 0, 0, 255);
SDL_RenderClear(ren);
SDL_SetRenderDrawColor(ren, 255, 0, 50, 255);
redraw(n-1,x,y,ren);
SDL_RenderPresent(ren);
break;
}
}
}
break;
}
}
SDL_Quit();
return(0);
}
编译使用
gcc -DDEBUG -c -Wall binter_polygon2ren.c | gcc binter_polygon2ren.o ../GCGraLib2/GCGraLib2.o -L/usr/X11R6/lib -lX11 -lSDL2 -lSDL2_ttf -lSDL2_image -lm -o binter_polygon2re
谢谢。
【问题讨论】：
-
至少知道 GDB 实际上能够告诉你什么是有帮助的 如果堆栈跟踪看起来很奇怪，那么很有可能你损坏了堆栈。
-
也许将程序分成几部分。从尝试做一些简单的事情开始，然后添加部分以达到您在此处尝试做的事情。
-
段错误发生在哪一行？
-
猜测，当你计算距离时，它应该是 while (i
标签： c segmentation-fault sdl