STL vector problem

sanguineraven · 2003-11-14T12:44:28

Ok so I''m working on Space Invaders using C++, SDL and STL. I have a "CSpriteBase" class which holds the base for a sprite (duh), which are its frames of animation, and the pauses between. So I declare: CSpriteBase Invader1; so I have declared the base for "invader1". In my initialisation for the game I do: sprbInvader1.init("data/invader1"); This loads the sprite frames from the directory given. So now the sprite base is setup. Now, I have CSprite. This is an actual sprite. As in it holds the x/y coordinates and has methods for moving the sprite around, drawing it to the screen etc. It has a protected member, a pointer to a CSpriteBase. Note: I also have a CEnemy class, which is derived from CSprite. This contains additional data related to specifically enemy sprites and enemy actions. It uses both the init and draw methods from CSprite so this cannot be the problem. So along with declaring my sprite base I also have: CEnemy test; And in my game initialisation I do: test.init(&sprbInvader1,40,40); This basically initialises the sprite so that it knows its an "invader1" sprite and it sets its x and y coords as 40. Then in my main game loop I call: test.draw(screen); Now this all works ok. It has the enemy object and it draws to the screen correctly at the right position. So now I move on. I create a vector: vector m_Enemies; So now I have an empty vector of enemies. I remove the code for the CEnemy object "test" from above and I now do: In the game initialisation: CEnemy temp; temp.init(&sprbInvader1,40,40); m_Enemies.push_back(temp); This in theory (as far as I understood) should create an enemy object, initialise it in the same way as the non-vector version, then "pushes"/"adds" it to the vector. So in theory I should have m_Enemies[0] as an enemy object right? Now when I add to the main loop: m_Enemies[0].draw(screen); The game runs but after a few milliseconds (when it comes to drawing) it closes, no errors, nothing. I''m pretty sure its a problem loading/initialising the frames for the sprite but I don''t know what I''m doing wrong. I also tried replacing the initialisation with: CEnemy temp; m_Enemies.push_back(temp); m_Enemies[0].init((&sprbInvader1,40,40); But this doesn''t work either. I really don''t know what I''m not doing right

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Started by sanguineraven November 13, 2003 08:01 PM

11 comments, last by sanguineraven 20 years, 5 months ago

Sabbac

122

November 14, 2003 11:01 AM

quote:Original post by Lektrix
In what way does "using STL" require a lot of copying?

What I mean by that is when you store something in a STL container you are truely storing a copy of the object. For any non-trivial class it costs more to copy an instance than copy a pointer.

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sanguineraven

725

Author

November 14, 2003 12:32 PM

quote:Original post by Sabbac
quote:Original post by sanguineraven
Yeah I''m using pointers at the moment. It''s a vector of pointers to CEnemy. But for some reason when I use the draw method, its data is incorrect

Ah-Ha!

I bet it looks like this:

void fn(){ CEnemy temp; temp.init(...); m_enemies.push_back(&temp);}void otherFn(){ m_enemies[0]->draw(...);}If so the problem is that when temp goes out of scope the pointer to temp becomes invalid.Try this instead: void fn(){ CEnemy* temp = new CEnemy; temp->init(...); m_enemies.push_back(temp);}void otherFn(){ m_enemies[0]->draw(...);}

hope that helps

[edit: speeling]

[edited by - sabbac on November 14, 2003 11:55:28 AM]

Yep!! That works, thankyou. I''ve been stuck on that for ages

Lektrix

106

November 14, 2003 12:44 PM

Remember that you will need to free the dynamically allocated memory that the std::vector''s pointer elements address. Alternatively, you could use a smart pointer.

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STL vector problem

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