c - Using `const` breaks program -

-

i wrote small test program using sdl 2.0 , opengl 1.1, , ran strange problem: making variables const breaks program! can explain why happens?

code

static float vertexes[] = { // static uint8_t colors[] = {  static float vertexes[] = { // no problem static const uint8_t colors[] = {  static const float vertexes[] = { // bad static const uint8_t colors[] = {  static const float vertexes[] = { // bad static uint8_t colors[] = {

respective screenshots

screen when neither constant screen when <code>colors</code> constant screen when <code>vertexes</code> constant screen when both constant

full (working) program

this program gives desired behaviour. comment out consts view broken versions.

// gcc -o main main.c -std=c11 -pedantic -wall -i. -lm -lmingw32 -lsdl2main -lsdl2 -lopengl32 -lglu32 -mwindows #include <sdl.h> #include <gl/gl.h> #include <gl/glu.h>  #include <stdio.h> #include <stdlib.h> #include <stdbool.h>  #define arraysize(arr) (sizeof(arr) / sizeof(*arr))  typedef struct {     float x;     float y;     float z; } vec3;  bool running; int width, height; sdl_window *window; sdl_glcontext ctx; vec3 rotation;  static /* const */ float vertexes[] = {      1.0f,  1.0f,  1.0f,      1.0f, -1.0f, -1.0f,      1.0f,  1.0f, -1.0f,      1.0f, -1.0f, -1.0f,      1.0f,  1.0f,  1.0f,      1.0f, -1.0f,  1.0f,      -1.0f, -1.0f, -1.0f,     -1.0f, -1.0f,  1.0f,     -1.0f,  1.0f,  1.0f,     -1.0f, -1.0f, -1.0f,     -1.0f,  1.0f,  1.0f,     -1.0f,  1.0f, -1.0f,       1.0f, -1.0f,  1.0f,     -1.0f, -1.0f, -1.0f,      1.0f, -1.0f, -1.0f,      1.0f, -1.0f,  1.0f,     -1.0f, -1.0f,  1.0f,     -1.0f, -1.0f, -1.0f,       1.0f,  1.0f,  1.0f,      1.0f,  1.0f, -1.0f,     -1.0f,  1.0f, -1.0f,      1.0f,  1.0f,  1.0f,     -1.0f,  1.0f, -1.0f,     -1.0f,  1.0f,  1.0f,       1.0f,  1.0f,  1.0f,     -1.0f,  1.0f,  1.0f,      1.0f, -1.0f,  1.0f,     -1.0f,  1.0f,  1.0f,     -1.0f, -1.0f,  1.0f,      1.0f, -1.0f,  1.0f,       1.0f,  1.0f, -1.0f,     -1.0f, -1.0f, -1.0f,     -1.0f,  1.0f, -1.0f,      1.0f,  1.0f, -1.0f,      1.0f, -1.0f, -1.0f,     -1.0f, -1.0f, -1.0f, }; static /* const */ uint8_t colors[] = {     0x00, 0x00, 0xff,     0x00, 0x00, 0xff,     0x00, 0x00, 0xff,     0x00, 0x00, 0xff,     0x00, 0x00, 0xff,     0x00, 0x00, 0xff,      0x00, 0x7f, 0x3f,     0x00, 0x7f, 0x3f,     0x00, 0x7f, 0x3f,     0x00, 0x7f, 0x3f,     0x00, 0x7f, 0x3f,     0x00, 0x7f, 0x3f,      0xff, 0xff, 0xff,     0xff, 0xff, 0xff,     0xff, 0xff, 0xff,     0xff, 0xff, 0xff,     0xff, 0xff, 0xff,     0xff, 0xff, 0xff,      0xff, 0xff, 0x00,     0xff, 0xff, 0x00,     0xff, 0xff, 0x00,     0xff, 0xff, 0x00,     0xff, 0xff, 0x00,     0xff, 0xff, 0x00,      0xff, 0xb3, 0x00,     0xff, 0xb3, 0x00,     0xff, 0xb3, 0x00,     0xff, 0xb3, 0x00,     0xff, 0xb3, 0x00,     0xff, 0xb3, 0x00,      0xff, 0x00, 0x00,     0xff, 0x00, 0x00,     0xff, 0x00, 0x00,     0xff, 0x00, 0x00,     0xff, 0x00, 0x00,     0xff, 0x00, 0x00, };  void onresize(void) {     glviewport(0, 0, width, height);     glmatrixmode(gl_projection);     glloadidentity();     gluperspective(60, (float)width/(float)height, 1, -1); }  void init(void); void fini(void);  void loop(void);  void handle(void); void render(void); void update(void);  int main(int argc, char* argv[]) {     init();     loop();     fini();      return 0; }  void init(void) {     sdl_displaymode mode;      if (sdl_init(sdl_init_video)) return;      sdl_getdesktopdisplaymode(0, &mode);     width = mode.w;     height = mode.h;     window = sdl_createwindow(         "game",         sdl_windowpos_undefined,         sdl_windowpos_undefined,         width,         height,         sdl_window_opengl | sdl_window_fullscreen     );     if (!window) return;     ctx = sdl_gl_createcontext(window);     if (!ctx) return;      onresize();     glenable(gl_depth_test);      running = true; } void fini(void) {     if (ctx) sdl_gl_deletecontext(ctx);     if (window) sdl_destroywindow(window);      sdl_quit(); }  void loop(void) {     while (running) {         handle();         render();         update();     } }  void handle(void) {     sdl_event event;      while (sdl_pollevent(&event)) {         switch (event.type) {         case sdl_windowevent:             switch (event.window.event) {             case sdl_windowevent_resized:                 width = event.window.data1, height = event.window.data2;                 onresize();                  break;             }             break;         case sdl_quit:             running = false;             break;         default:             break;         }     } } void render(void) {     glclearcolor(0.9f, 0.8f, 0.7f, 1.0f);     glclear(gl_color_buffer_bit | gl_depth_buffer_bit);      glmatrixmode(gl_modelview);     glloadidentity();     glulookat(0, 0, -5, 0, 0, 0, 0, 1, 0);     glrotatef(rotation.x, 1, 0, 0);     glrotatef(rotation.y, 0, 1, 0);     glrotatef(rotation.z, 0, 0, 1);     glscalef(0.25f, 0.25f, 0.25f);      glcolor4f(0.0f, 0.0f, 0.0f, 0.0f);     glbegin(gl_lines);         glvertex3f(0.0f, 0.0f, 0.0f);         glvertex3f(9.0f, 0.0f, 0.0f);         glvertex3f(0.0f, 0.0f, 0.0f);         glvertex3f(0.0f, 9.0f, 0.0f);         glvertex3f(0.0f, 0.0f, 0.0f);         glvertex3f(0.0f, 0.0f, 9.0f);     glend();      glenableclientstate(gl_vertex_array);     glenableclientstate(gl_color_array);          glvertexpointer(3, gl_float, 0, vertexes);         glcolorpointer(3, gl_unsigned_byte, 0, colors);         gldrawarrays(gl_triangles, 0, arraysize(vertexes));      glenableclientstate(gl_color_array);     gldisableclientstate(gl_vertex_array);      sdl_gl_swapwindow(window); } void update(void) {     rotation.x++;     rotation.y++; }

alternatively available here.

use arraysize(vertexes) / 3 instead of arraysize(vertexes) in gldrawarrays() call.

gldrawarrays()'s count argument number of vertices, not number of floats. right you're telling opengl read off end of vertexes/colors arrays $diety-knows-what. you're lucky isn't segfaulting.

const/non-const switching segment arrays ending in, providing different "garbage" vertices opengl try interpret.


Comments

Post a Comment

Popular posts from this blog

javascript - Slick Slider width recalculation -

-
i'm trying add slide in panel on slick container css. carousel works except new width not being calculated when space has been added. recalibrate once advance next slide i'd happen each time panel opened or closed. i've tried adding both margin , padding, neither makes difference. ideas? https://jsfiddle.net/mhigley/dpf7mlpl/ html: <button type="button" id="button"><i class="fa fa-arrow-right"></i></button> <aside> <h2>slide in panel</h2> <ol> <li>list item</li> <li>list item</li> <li>list item</li> <li>list item</li> <li>list item</li> </ol> </aside> <main role="main"> <div class="sections"> <section> <article> <h2>first slide</h2> <p>lorem ipsum d...
Read more

jsf - PrimeFaces Datatable - What is f:facet actually doing? -

-
looking through primefaces code in app noticed following line: <f:facet name="header">#{trainsearch.traincount} trains</f:facet> it looks overriding header, makes sense, can explain me in little more detail? what happening line of code? complete code listed below: <p:datatable id = "results" value = "#{trainsearch.trains}" var = "train" rendered="#{not empty trainsearch.trains}" styleclass = "train-search-table horizontal-border"> <f:facet name="header">#{trainsearch.traincount} trains</f:facet> <p:column headertext = "train id"> <p:panelgrid columns="1" styleclass = "train-id-grid" layout = "grid"> <h:outputtext styleclass = "train-id-label" value="#{train.traini}"/> <h:outputtex...
Read more

angular2 services - Angular 2 RC 4 Http post not firing -

-
i trying fire post request app , it's not working, tried multiple ways. don't see request being fired under network tab in chrome. not sure problem is, appreciated. import { injectable } '@angular/core'; import { http, headers } '@angular/http'; @injectable() export class userservice{ private _url="users"; constructor(private _http: http){ } checkifusernameexists(username){ return this._http.get(this._url+"/"+username) .map(response => response.json()) } createuser(user){ let headers = new headers(); headers.append('content-type', 'application/json') console.log(json.stringify(user)); return this._http.post(this._url, json.stringify(user),{headers: headers}) .map(response => response.json()) } } first need capture error , solve error: this._http.post(this._url, json.stringify(user),{headers: headers}) .subscribe( ...
Read more