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Drawing Text Access Violation using SFML

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#1 Gaius Baltar   Members   -  Reputation: 223

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Posted 13 August 2014 - 07:28 PM

call stack:
 
> sfml-graphics-d-2.dll!std::_Tree<std::_Tmap_traits<unsigned int,sf::Font::Page,std::less<unsigned int>,std::allocator<std::pair<unsigned int const ,sf::Font::Page> >,0> >::_Lbound(const unsigned int & _Keyval) Line 2109 C++
  sfml-graphics-d-2.dll!std::_Tree<std::_Tmap_traits<unsigned int,sf::Font::Page,std::less<unsigned int>,std::allocator<std::pair<unsigned int const ,sf::Font::Page> >,0> >::lower_bound(const unsigned int & _Keyval) Line 1575 C++
  sfml-graphics-d-2.dll!std::map<unsigned int,sf::Font::Page,std::less<unsigned int>,std::allocator<std::pair<unsigned int const ,sf::Font::Page> > >::operator[](const unsigned int & _Keyval) Line 226 C++
  sfml-graphics-d-2.dll!sf::Font::getGlyph(unsigned int codePoint, unsigned int characterSize, bool bold) Line 295 C++
  sfml-graphics-d-2.dll!sf::Text::ensureGeometryUpdate() Line 269 C++
  sfml-graphics-d-2.dll!sf::Text::getLocalBounds() Line 214 C++
  Engine.exe!Text::getLocalBounds() Line 41 C++
  Engine.exe!Button::setTextSize(unsigned int textSize) Line 56 C++
  Engine.exe!Button::setString(std::basic_string<char,std::char_traits<char>,std::allocator<char> > text) Line 47 C++
  Engine.exe!Button::Button(std::basic_string<char,std::char_traits<char>,std::allocator<char> > text, unsigned int textSize, sf::Vector2<float> pos, sf::Color textColor, sf::Color buttonFaceColor) Line 7 C++
  Engine.exe!Missile_Command::initButtons() Line 56 C++
  Engine.exe!Missile_Command::init() Line 29 C++
  Engine.exe!Missile_Command::Missile_Command() Line 6 C++
  Engine.exe!main() Line 4 C++
  [External Code]
  [Frames below may be incorrect and/or missing, no symbols loaded for kernel32.dll]
 
code:
 

void Text::draw(sf::RenderTarget & target, sf::RenderStates states) const{
target.draw(text);
}

 
which was called by:
 

void Button::draw(sf::RenderTarget & target, sf::RenderStates states) const{
target.draw(buttonFace);
target.draw(text);
}

 
No pointers were used to my knowledge.
 
 
The exact error is as follows:
Unhandled exception at 0x0F21F95C (sfml-graphics-d-2.dll) in Engine.exe: 0xC0000005: Access violation reading location 0x0000000D.
 
I've been trying to solve this for quite some time now. I think it has something to do with my sf::Text object not being properly initialized or something, but I couldn't find anything.

 

 
Here's the my Text class if anyone's interested:
 

Spoiler

 
"text" and "font" are private class members.



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#2 dejaime   Crossbones+   -  Reputation: 4002

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Posted 13 August 2014 - 08:09 PM

How are you using it? Could you post the code where you actually configure the text you're using?

The sf::Text depends on the font you're passing on to it, it stores just a pointer to it, so you must make sure that pointer is valid (as in not destroy the font before destroying the text).

So, how are you passing that font along? Are you, by any chance using something like myFont.getFont() ? It looks like you may be passing a font that is valid at a given time, but then comes out of scope and generates undefined behavior.


Edited by dejaime, 13 August 2014 - 10:01 PM.


#3 Gaius Baltar   Members   -  Reputation: 223

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Posted 14 August 2014 - 10:34 AM

Ok, I think I found the source of the problem.

_quit = ui::Button("Quit", 32, sf::Vector2f(0, 200), sf::Color::Black, "segoeuil.ttf");
_start = ui::Button("Start", 32, sf::Vector2f(0, 300), sf::Color::Black, "segoeuil.ttf");

For some reason, re instantiating the Button objects and then drawing them gives me the out of range error.

I found that if I immediately instantiated the Button objects the error wouldn't appear.

 

I made a minimal working example to demonstrate.

 

main.cpp:

#include <SFML/Graphics.hpp>
class Text : public sf::Drawable
{
	sf::Font font;
	sf::Text text;
public:
	Text(std::string string){
		if (!font.loadFromFile("segoeuil.ttf")) // Nothing wrong with loading the font
			std::exit(-1);
		text = sf::Text(string, font, 30);
	}
	Text(){ }

	virtual void draw(sf::RenderTarget & target, sf::RenderStates states) const{
		target.draw(text);
	}
};

int main(){
	sf::RenderWindow window(sf::VideoMode(800, 600), "Text test");

	Text text("Text");
        //Text text; -> same result

	// Error (on draw) -> Access Violation
	// Commenting this line out, solves the problem
	text = Text("Text");

	while (window.isOpen()){
		window.clear();
		window.draw(text);
		window.display();
	}

	return 0;
}

Edit: Solved! I was missing a = operator overload, because SFML stores it's fonts as pointers in it's text objects.

 

so this is what I added to make the above code work:

Text& operator=(Text other){
	font = other.font;
	text = other.text;
	text.setFont(font);
	return *this;
}

Edited by Gaius Baltar, 14 August 2014 - 11:09 AM.






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