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Access Violation Issue

Started by SleepyRhino Jul 27, 2014 at 9:16 AM 2 replies 1.6k views

Original Post

SleepyRhino

Jul 27, 2014 at 9:16 AM

I am having an issue and can't seem to resolve it.

Here is the code

FontCache.h


#pragma once

#include <SFML/Graphics/Font.hpp>

#include <unordered_map>
#include <memory>
#include <string>

class FontCache
{
public:
	typedef std::shared_ptr<sf::Font> FontPtr;
	typedef std::unordered_map<std::string, FontPtr> FontMap;
	typedef FontMap::iterator FontMapIterator;

public:
	FontCache(unsigned int size = 10);
	~FontCache();
	bool add(std::string name, std::string file);
	void remove(std::string name);
	sf::Font& get(std::string name);
	void unload();

private:
	FontMap resources_;
};

FontCache.cpp


#include "StandardInc.h"
#include "FontCache.h"
#include "PhysFsStream.h"

FontCache::FontCache(unsigned size)
: resources_(size)
{
	
}

FontCache::~FontCache()
{
	unload();
}

bool FontCache::add(std::string name, std::string file)
{
	FontMapIterator it = resources_.find(name);

	if(it != resources_.end())
	{
		return true;
	}

	PhysFsStream stream;
	stream.open(file.c_str());

	FontPtr newFont = std::make_shared<sf::Font>();
	if (!newFont->loadFromStream(stream))
	{
		printf("Error: Unable to load %s\n", file.c_str());
		return false;
	}

	resources_[name] = std::move(newFont);
	printf("Added Font: %s\n", file.c_str());
	return true;
}

void FontCache::remove(std::string name)
{
	FontMapIterator it = resources_.find(name);

	if(it != resources_.end())
	{
		resources_.erase(it);
	}
}

sf::Font& FontCache::get(std::string name)
{
	FontMapIterator it = resources_.find(name);
	if(it == resources_.end())
		add(name, name);

	return *resources_[name];
}

void FontCache::unload()
{
	resources_.clear();
}

Part of GameScene.hpp


    sf::Text buildDetails_ = new sf::Text();
    buildDetails_->setFont(fonts_.get("fonts/PTM55FT.ttf"));
    buildDetails_->setString("Build 0.0.0");
    buildDetails_->setPosition(10, 10);

Whenever I try to use the font with an sf::Text class I get an access violation error, I have tried making a simple version of the code and not using the FontCache class and basically copied and pasted the code from the FontCache class into the GameScene class where the sf::Text is being created and it worked fine.

Any ideas on what might be cause this would be great my mind has gone blank tryign to fix it.

rip-off

Jul 27, 2014 at 10:12 AM

Have you tried running your code in a debugger? For example, one thing that could be happening is that one of the error paths in FontCache::add is being triggered, but FontCache::get is not checking for such errors.

SleepyRhino

Jul 27, 2014 at 10:25 AM

Yes the font is added to the map and retrieved from the map fine.

Seems like the error is being thrown from within the SFML graphics dll.

So I have built SFML so I could get the pdb files to do abit of deeper digging.

At this call in the Font::loadGlyph is where he trouble starts


    // Load the glyph corresponding to the code point
    if (FT_Load_Char(face, codePoint, FT_LOAD_TARGET_NORMAL | FT_LOAD_FORCE_AUTOHINT) != 0)
        return glyph;

And the if (static_cast(stream->seek(offset)) == offset) line is where is fails.


    // FreeType callbacks that operate on a sf::InputStream
    unsigned long read(FT_Stream rec, unsigned long offset, unsigned char* buffer, unsigned long count)
    {
        sf::InputStream* stream = static_cast<sf::InputStream*>(rec->descriptor.pointer);
        if (static_cast<unsigned long>(stream->seek(offset)) == offset)
        {
            if (count > 0)
                return static_cast<unsigned long>(stream->read(reinterpret_cast<char*>(buffer), count));
            else
                return 0;
        }
        else
            return count > 0 ? 0 : 1; // error code is 0 if we're reading, or nonzero if we're seeking
    }

So when SFML is checking the Font pointer is it fine and can access it but when it gets to here I get an Access violation error.

ChaosEngine

Jul 27, 2014 at 9:23 PM

And the if (static_cast(stream->seek(offset)) == offset) line is where is fails.

Is stream a valid pointer at that point? You should be able to look at it in the debugger and see some sensible values for each member.

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