Esc detector wont run -- 'out of scope'

SDL Development
1

For what ever reason I get an out of scope error with the following key presser

Code:

while (gameRunning)
{
if (SDL_PollEvent(&event))
{
if (event.type == SDL_QUIT)
{
gameRunning = false;
}

     if (event.type == SDL_KEYDOWN)
     {
        SDL_Key keyPressed = event.key.keysym.sym;

        switch (keyPressed)
        {
           case SDLK_ESCAPE:
              gameRunning = false;
              break;
        }
     }
  }

}

Code:

…\src\drawLine.cpp:39:13: error: ‘SDLKey’ was not declared in this scope
SDLKey keyPressed = event.key.keysym.sym;
^
…\src\drawLine.cpp:41:21: error: ‘keyPressed’ was not declared in this scope
switch (keyPressed)

Got to be something simple!

2

Try “SDL_Keycode”.

-H-----
“After you finish the first 90% of a project, you have to finish the
other 90%.” - Michael Abrash

3

If this is SDL2, then check: https://wiki.libsdl.org/SDL_Keysym

Your type should probably be SDL_Keycode.

4

Thanks! That fixed it so it will compile. No more errors. The code still doesn’t do what it is supposed to: abort when you press esc. I flagged it up. It never gets passed flag 1.

Code:

#include
#include"SDL.h"
using namespace std;

const int WINDOW_WIDTH = 640;
const int WINDOW_HEIGHT = 480;
const char* WINDOW_TITLE = “SDL Start”;

int main(int argc, char **argv)
{ cout<<“flag 0”;
SDL_Init( SDL_INIT_VIDEO );

SDL_Event event;

bool gameRunning = true;

while (gameRunning)
{
cout<<“flag 1”<<endl;
if (SDL_PollEvent(&event))
{
cout<<“flag 2”;
if (event.type == SDL_QUIT)
{
cout<<“flag 3”;
gameRunning = false;
}

     if (event.type == SDL_KEYDOWN)
     {

        SDL_Keycode keyPressed = event.key.keysym.sym;

        switch (keyPressed)
        {
           case SDLK_ESCAPE:
              gameRunning = false;
              break;
        }
     }

  }

}

SDL_Quit();

cout<<endl<<“end flag”;
return 0;

}

5

Sorry: forgot to post output:
flag 1
flag 1
flag 1
flag 1
flag 1
flag 1
flag 1
…ad infinitum

gameRunning is never set to false

6

Try:

while(SDL_PollEvent(&event)) …

Instead of using an if statement.

That will loop through the event queue on each iteration of the main while
loop.

7

Do you have a window open? Does Control-C work?

8

My console window is open and its just producing flag 1. I changed the
if to while as suggested – no changed.
Cntrl - C no change.–

Gray Family

@Clangray

9

And the other behavior is that if I don’t click - ‘focus’ into the
console my keypresses will show up in my IDE.–

Gray Family

@Clangray

10

capehill wrote:

Do you have a window open? Does Control-C work?

I’d like to second the above.

Many platforms need a window open, before input can be received. Using either SDL_CreateWindowAndRenderer, or just SDL_CreateWindow, once beforehand at app init, may be sufficient to fix this.

– David L.

11

I agree also. I thought there was some caveat that you needed a window open
to receive input events.

12

Ok, I introduced a window

#include"SDL.h"

using namespace std;

const char* WINDOW_TITLE = “SDL Start”;

int main(int argc, char **argv)

{

SDL_Init(SDL_INIT_EVERYTHING);

SDL_Window * window = nullptr;

    window = SDL_CreateWindow("Hello World!",

                              SDL_WINDOWPOS_CENTERED,

                              SDL_WINDOWPOS_CENTERED,

                              640,480,

                              SDL_WINDOW_SHOWN);



    SDL_Delay(2000); // Delay so that we can see the

SDL_Event event;

cout<<“flag 0”;

bool gameRunning = true;

while (gameRunning)

{

cout<<“flag 1”<<endl;

  while (SDL_PollEvent(&event))

  {

   gameRunning = false;

   cout<<"flag 2";

   if (event.type == SDL_QUIT)

      {

   cout<<"flag 3";

   gameRunning = false;

   }



     while (event.type == SDL_KEYDOWN)

     {

      cout<<"flag 2";

        SDL_Keycode keyPressed = event.key.keysym.sym;



        switch (keyPressed)

        {

           case SDLK_ESCAPE:

              gameRunning = false;

              break;

        }

     }



  }

}

SDL_Quit();

cout<<endl<<“end flag”;

return 0;

}

I’m getting flag2 constantly.

Esc and other keys seem to have no effect

**if I substitute if for while (below)

change while back to if

if (SDL_PollEvent(&event))

output:

flag 0flag 1

flag 2

end flag–

Gray Family

@Clangray

13

As typed, your while(event.type == SDL_KEYDOWN) is an infinite loop.

Jonny D

14

Thx. Its infinite only under certain circumstances, which is
confounding. What are you seeing and how can I fix it.
If I use “if”:

if (SDL_PollEvent(&event))

its not infinite

if I use while

while(SDL_PollEvent(&event))

if is

flag 2, flag 2 ad infinitum

Does the window have to be in the loop to get the benefit of the
key stroke?–

Gray Family

@Clangray

15

Thanks every one. In addition to having a window in context I added this small code:

Code:

const Uint8 *keys = SDL_GetKeyboardState(NULL);
SDL_Event e;
.
.
.

while (SDL_PollEvent(&e)){
if (e.type == SDL_QUIT){
done = SDL_TRUE;
}
if (keys[SDL_SCANCODE_ESCAPE]){
done = SDL_TRUE;}
}

16

Checking scancodes is a different thing than handling events. Unless
necessary to achieve an effect (e.g. holding a key while moving the mouse),
you should only be using the event structure when in the SDL_PollEvent loop.

Jonny D

17

thx a bunch, i get that now