Thread: why does my array get bigger?

here is a C program for windows

Code:

#include <windows.h>
#include <gl/gl.h>
#include <stdlib.h>
#include <stdio.h>
LRESULT CALLBACK WindowProc(HWND, UINT, WPARAM, LPARAM);
void EnableOpenGL(HWND hwnd, HDC*, HGLRC*);
void DisableOpenGL(HWND, HDC, HGLRC);
int true=1;
struct block
{
float x;
float y;
int exists;
float trecy;
};

struct block *block_array;

void add_to_array(struct block array_pointer[],struct block*obj_pointer)
{
    float array_size=sizeof(&array_pointer);
    printf("array size is %f",array_size);
    float obj_size=sizeof(&obj_pointer);
    printf("object size is %f",obj_size);

}
int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    WNDCLASSEX wcex;
    HWND hwnd;
    HDC hDC;
    HGLRC hRC;
    MSG msg;
    BOOL bQuit = FALSE;
    float theta = 0.0f;

    /* register window class */
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_OWNDC;
    wcex.lpfnWndProc = WindowProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = "GLSample";
    wcex.hIconSm = LoadIcon(NULL, IDI_APPLICATION);;


    if (!RegisterClassEx(&wcex))
        return 0;

    /* create main window */
    hwnd = CreateWindowEx(0,
                          "GLSample",
                          "OpenGL Sample",
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          800,
                          600,
                          NULL,
                          NULL,
                          hInstance,
                          NULL);

    ShowWindow(hwnd, nCmdShow);

    /* enable OpenGL for the window */
    EnableOpenGL(hwnd, &hDC, &hRC);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glClearColor(0, 0, 0, 0);
    glOrtho (0,800,600 , 0, 0, 1);
    glDisable(GL_DEPTH_TEST);
    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.375, 0.375, 0);
    glEnable(GL_BLEND);
    glEnable(GL_TEXTURE_2D);
   glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
   srand(1);
block_array = malloc(1 * sizeof(struct block));

   add_to_array(block_array,&block_array[0]);
   float x=0;
   float y=0;
            int block_iter=0;
            for (x=40;x<800;x=x+80)
            {
            for (y=30;y<600;y=y+60)
            {
               block_array[block_iter].exists=true;
               block_array[block_iter].x=x;
               block_array[block_iter].y=y;
               block_iter++;
            }
            }
    /* program main loop */
    while (!bQuit)
    {
        /* check for messages */
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            /* handle or dispatch messages */
            if (msg.message == WM_QUIT)
            {
                bQuit = TRUE;
            }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        else
        {
            /* OpenGL animation code goes here */

            glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
            glClear(GL_COLOR_BUFFER_BIT);

            //glPushMatrix();
            //glRotatef(theta, 0.0f, 0.0f, 1.0f);
            float x=0;
            float y=0;
            int block_iter=0;
            for (x=40;x<800;x=x+80)
            {
            for (y=30;y<600;y=y+60)
            {

             glLoadIdentity();
    glTranslatef(0.375, 0.375, 0);
    glTranslatef(block_array[block_iter].x,block_array[block_iter].y,0);
    glRotatef(block_array[block_iter].x,0,0,1);

            glBegin(GL_QUADS);

                glColor3f(.3f, .3f, .3);
                   glVertex2f(-40,-30);
                glColor3f(.60f, .60f, .60f);
                glVertex2f(40, -30);
                glColor3f(0.9f, 0.9f, 0.9f);
                glVertex2f(40,30);
                glColor3f(0.60f, 0.60f, 0.60f);
                glVertex2f(-40,30);

            glEnd();
            block_iter++;
            }
            }

            //?//glPopMatrix();

            SwapBuffers(hDC);

            theta += 1.0f;
            Sleep (1);
        }
    }

    /* shutdown OpenGL */
    DisableOpenGL(hwnd, hDC, hRC);

    /* destroy the window explicitly */
    DestroyWindow(hwnd);

    return msg.wParam;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
        case WM_CLOSE:
            PostQuitMessage(0);
        break;

        case WM_DESTROY:
            return 0;

        case WM_KEYDOWN:
        {
            switch (wParam)
            {
                case VK_ESCAPE:
                    PostQuitMessage(0);
                case 0x41: //a
                    block_array[1].y++;//'=block_array[10].y+20.0;
                    printf("%f\n",block_array[10].y);
                    break;
                case 0x51: //q

                break;
            }
        }
        break;

        default:
            return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }

    return 0;
}

void EnableOpenGL(HWND hwnd, HDC* hDC, HGLRC* hRC)
{
    PIXELFORMATDESCRIPTOR pfd;

    int iFormat;

    /* get the device context (DC) */
    *hDC = GetDC(hwnd);

    /* set the pixel format for the DC */
    ZeroMemory(&pfd, sizeof(pfd));

    pfd.nSize = sizeof(pfd);
    pfd.nVersion = 1;
    pfd.dwFlags = PFD_DRAW_TO_WINDOW |
                  PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
    pfd.iPixelType = PFD_TYPE_RGBA;
    pfd.cColorBits = 24;
    pfd.cDepthBits = 16;
    pfd.iLayerType = PFD_MAIN_PLANE;

    iFormat = ChoosePixelFormat(*hDC, &pfd);

    SetPixelFormat(*hDC, iFormat, &pfd);

    /* create and enable the render context (RC) */
    *hRC = wglCreateContext(*hDC);

    wglMakeCurrent(*hDC, *hRC);
}

void DisableOpenGL (HWND hwnd, HDC hDC, HGLRC hRC)
{
    wglMakeCurrent(NULL, NULL);
    wglDeleteContext(hRC);
    ReleaseDC(hwnd, hDC);
}

its supposed to crash because the array is only 1 element long, if you comment out the call to 'add_to_array' it will crash as its supposed to.
Why does add_to_array grow the array?

thanks for the reply

what is wrong with the add_to_array function that would cause this behaviour?

yes, originally I wanted to write a function that added an object to the first empty space in the array, or if the array was full...create a new larger array and copy the objects to the new larger array (and dispose of the old one)

so then , just to make sure I understood the language I decided to reduce the array size to 1 and then it didnt crash so I got worried.

What Im worried about is 'the future' what If I make a mistake and I am not warned...instead the program will do 'undefined behaviour' and I wont have a clue what is going wrong.

It would help me to know what is causing the error in the (badly named) function

I am guessing that the sizeof is not returning what you expect.

I created a test program below that my help if the above is the problem.

Tim S.

Code:

#include <stdio.h>
#include <stdlib.h>

struct block
{
 float x;
 float y;
 int exists;
 float trecy;
};

struct block *block_array;

int main()
{

    block_array = malloc(1 * sizeof(struct block));

    printf("sizeof: %d \n", sizeof(struct block));
    printf("sizeof block_array: %d \n", sizeof(block_array));
    printf("sizeof block_array: %d \n", sizeof(*block_array));
    printf("sizeof block_array: %d \n", sizeof(*block_array)/sizeof(struct block));
    return 0;
}