使用指向我的数组的指针可以让我C++"Unhandled exception"?
Using a pointer to my arrays gives me an "Unhandled exception" in C++?
以下是供参考的完整代码:
#include <SDL.h> /* SDL stuff */
#include <SDL_video.h> /* surfaces,screen,renderer */
#include <SDL_keyboard.h> /* to handle kbd input */
#include <cstdlib> /*srand,rand*/
#include <iostream> /* cout,cin */
#include <time.h> /* time */
#define NUMFLAKES 128
#define NUMLOOPS (NUMFLAKES >> 1)
//setup the putpixel function
void putpixel( SDL_Renderer* renderer,int &x,int &y,SDL_Color &pxl )
{
SDL_SetRenderDrawColor( renderer, pxl.r,pxl.g,pxl.b,pxl.a );
SDL_RenderDrawPoint( renderer,x,y );
}
int quitFunc( SDL_Surface *screen,SDL_Texture *texdisp,SDL_Renderer *renderer,SDL_Window *window );
int main( int argc,char *args[] )
{
std::ios::sync_with_stdio( false ); //make iostream a bit snappier by stopping sync with stdio
//Start SDL
int initret = SDL_Init( SDL_INIT_VIDEO | SDL_INIT_EVENTS );
switch( initret ) {
case true:
std::cout << "SDL_Init: Couldn't start SDL...n" << SDL_GetError() << std::endl; break;
default: break;
}
SDL_DisplayMode fulldisp;
SDL_GetCurrentDisplayMode( 0,&fulldisp );
//The attributes of the screen
const int PX_WIDTH = (int)(fulldisp.w / 1.5);
const int PX_HEIGHT = (int)(fulldisp.h / 1.5);
int xo[NUMFLAKES] = {};
int yo[NUMFLAKES] = {};
int *x = &xo[NUMFLAKES]; //fix this bullshit
int *y = &yo[NUMFLAKES];
//To define the current window
SDL_Window* window = SDL_CreateWindow( "SDL Snowflakes",
SDL_WINDOWPOS_UNDEFINED,SDL_WINDOWPOS_UNDEFINED,
PX_WIDTH,PX_HEIGHT,SDL_WINDOW_SHOWN );
//The surface using the window defined above
SDL_Surface* screen = SDL_GetWindowSurface( window );
SDL_ShowCursor(1);
/* Set up renderer */
SDL_Renderer* renderer = SDL_CreateRenderer( window,-1,
SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE | SDL_RENDERER_PRESENTVSYNC );
/* render to texture */
SDL_Texture* texdisp = SDL_CreateTexture(renderer,SDL_PIXELFORMAT_RGB888,
SDL_TEXTUREACCESS_TARGET,PX_WIDTH,PX_HEIGHT);
SDL_SetRenderTarget( renderer,texdisp );
SDL_UpdateWindowSurfaceRects( window,NULL,NUMFLAKES );
SDL_SetRenderDrawColor( renderer,0,0,0,0 );
SDL_RenderClear( renderer );
//colours for putpixel
SDL_Color white;
SDL_Color rndcol;
white = { 0xFF,0xFF,0xFF,0xFF };
rndcol = { rand() % 255,rand() % 255,rand() % 255,0xFF };
//If there was an error in setting up the screen
switch((bool)(screen)) {
case 0:
SDL_Quit(); return 1; break;
default:
std::cout << "Created window of size: " << PX_WIDTH << "x" << PX_HEIGHT << std::endl;
break;
}
SDL_Event sdlevent;
SDL_PollEvent( &sdlevent );
//Setup Snow Flakes
SDL_Rect putfr; //Rect for updating the screen
int flake = NUMFLAKES;
int *pFlake = &flake;
srand( ( unsigned )time( NULL ) );
for( *pFlake = 0; *pFlake < NUMFLAKES; (*pFlake)++ )
{
(*x)[ pFlake ] = rand() % PX_WIDTH;
(*y)[ pFlake ] = rand() % ( int )( PX_HEIGHT / 1.5 );
xo[ *pFlake ] = (*x)[ pFlake ];
yo[ *pFlake ] = (*y)[ pFlake ];
std::cout << "Set origin..." << (*x)[ pFlake ] << "," << (*y)[ pFlake ]
<< "nAt address->" << y[ *pFlake ] << "," << y[ *pFlake ] << std::endl;
putpixel( renderer,(*x)[ pFlake ],(*y)[ pFlake ],white );
/* Intended to only update what changed on screen, still working on it, ignore this */
putfr.x = (*x)[ pFlake ];
putfr.y = (*y)[ pFlake ];
SDL_SetRenderTarget( renderer,NULL );
SDL_RenderCopy( renderer,texdisp,NULL,&putfr );
SDL_RenderPresent( renderer );
}
int move,movex,movey;
for( int loop = 0; loop <= NUMLOOPS && (bool)(sdlevent.type != SDL_QUIT); loop++ )
{
for( (*pFlake) = 0; (*pFlake) < NUMFLAKES && sdlevent.type != SDL_QUIT; (*pFlake)++,SDL_PollEvent( &sdlevent ) )
{
//resetting rndcol
rndcol = { rand() % 255,rand() % 255,rand() % 255 };
// choose whether to move left, right or straight down and by how many pixels
move = rand() % 3;
movex = ( rand() % 2 ) + 1;
movey = ( rand() % 5 ) + 1;
//backup the existing positions
xo[ *pFlake ] = (*x)[ pFlake ];
yo[ *pFlake ] = (*y)[ pFlake ];
// now draw again
putpixel( renderer,(*x)[ pFlake ],(*y)[ pFlake ],rndcol );
// move down the screen by the no of movey
if( (*y)[ pFlake ] + ( movey + 1 ) < PX_HEIGHT )
{
(*y)[ pFlake ] = (*y)[ pFlake ] + ( movey + 1 );
} else {
putpixel( renderer,(*x)[ pFlake ],(*y)[ pFlake ],rndcol );
(*y)[ pFlake ] = rand() % ( PX_HEIGHT / 2 );
}
if( (*x)[ pFlake ] < 0 ) {
(*x)[ pFlake ] = movex;
}
if( (*x)[ pFlake ] > PX_WIDTH ) {
(*x)[ pFlake ] = ( PX_WIDTH - movex );
}
// if 0 then left, 1 for right, else straight down
switch( move ) {
case 0:
(*x)[ &pFlake ] = (*x)[ &pFlake ] - movex; break;
case 1:
(*x)[ &pFlake ] = (*x)[ &pFlake ] + movex; break;
}
putpixel( renderer,(*x)[ pFlake ],(*y)[ pFlake ],rndcol );
}
//Renderer needs only to update what changes
putfr.x = xo[ *pFlake ];
putfr.y = yo[ *pFlake ];
SDL_SetRenderTarget( renderer,NULL );
SDL_RenderCopy( renderer,texdisp,&putfr,&putfr );
SDL_RenderPresent( renderer );
SDL_Delay(128);
//std::cout << "Completed " << loop << " loops" << std::endl;
}
quitFunc( screen,texdisp,renderer,window );
return 0; //just to stop compiler warning
}
int quitFunc( SDL_Surface *screen,SDL_Texture *texdisp,SDL_Renderer *renderer,SDL_Window *window )
{
SDL_FreeSurface( screen ); // Destroy things before SDL_Quit
SDL_DestroyTexture( texdisp );
SDL_DestroyRenderer( renderer );
SDL_DestroyWindow( window );
std::cout << "nDestroyed SDL objects, calling SDL_Quit()..." << std::endl;
SDL_Quit();
std::cout << "nAccomplished SDL_Quitn" << std::endl;
return 0;
}
我正在尝试使用指向 x[] 和 y[](不是指针数组,而是指向数组的指针)的指针来使程序只使用这些对象,而不是制作副本并更改它们。
这几乎只是为了提高处理效率/最小化程序占用空间,因为数组在某些点可能会变得太大,并且复制这些点可能需要太多时间。
我也尝试过:
int *x = { &xo[NUMFLAKES] };
int *y = { &yo[NUMFLAKES] };
这给了我同样的错误。我知道我可能错误地使用了指针(我认为它试图访问错误的内存?),但我不确定如何以正确的方式做到这一点。
我怀疑问题是
int *x = &xo[NUMFLAKES];
这是初始化指针 x 以指向数组NUMFLAKES
元素的地址 - 一个超过数组末尾的地址。这不太可能是你的意思。也许
int *x = &xo[0]
?
这会将指针设置为数组第一个元素的地址,从而允许您使用 x
作为 xo
的别名。
错误在这里:int *x = &xo[NUMFLAKES];
您正在尝试访问大小为 128 的数组的索引 128(NUMFLAKES)。此指数 (128) 超出界限,因为索引从 0 开始。
您可以通过以下方式实现所需的目标:
int *p;
int xo[NUMFLAKES];
p = xo; // <-- Now p is pointing to the first element of xO
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