TIER 2 : Inserting a new element into unordered_map or map give access violation error

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nickydemon

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Posted: 28th Jul 2020 16:56 Edited at: 28th Jul 2020 16:57

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Hi, I am currently using tier 2 of AGKS. I am trying to implementing a simple scene system by referencing this guy tutorial :
http://thatgamesguy.co.uk/cpp-game-dev-6/

I have done this in another library like raylib and it works well. But in app game kit tier2, it gave me access violation error whenever I try to insert new element in unordered_map or map.
For example, I create an unorder_map in the class app in template.h and insert new element in begin() method in template.cpp

+ Code Snippet

void app::Begin(void)
{
	if ( agk::GetRenderer() )
	{
		agk::SetVirtualResolution (1024, 768);
		agk::SetClearColor( 151,170,204 ); // light blue		
		agk::SetScissor(0,0,0,0);
	}

	_test.insert(std::pair<const char*, int>("Hello", 10));
}

After executing it just showed that I have access violation. To be honest I have no idea what is happening. Am I doing something wrong?

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Xaron

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Posted: 29th Jul 2020 07:57

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Can you show a bit more of the code? Where is _test created, what is it?

Beside that it's often better to use "emplace" instead of "insert" nowadays.

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nickydemon

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Posted: 29th Jul 2020 08:07

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Hi Xaron, I am sorry that I provided too less of my code. The _test variable is created inside template.h

+ Code Snippet

#ifndef _H_AGK_TEMPLATE_
#define _H_AGK_TEMPLATE_

// Link to GDK libraries
#include "AGK.h"

#define DEVICE_WIDTH 1024
#define DEVICE_HEIGHT 768
#define DEVICE_POS_X 32
#define DEVICE_POS_Y 32
#define FULLSCREEN false

// used to make a more unique folder for the write path
#define COMPANY_NAME "My Company"


#include <unordered_map>



// Global values for the app
class app
{
private:
	
	std::unordered_map<const char*, int> _test;
	std::vector<int> _hello;

public:

	// constructor
	app() { memset ( this, 0, sizeof(app)); }

	// main app functions - mike to experiment with a derived class for this..
	void Begin( void );
	int Loop( void );
	void End( void );


};

extern app App;

#endif

// Allow us to use the LoadImage function name
#ifdef LoadImage
 #undef LoadImage
#endif

Below is the error showed when in debugging mode. Please refer attached file. It's in japanese and the message just stated that An exception has been thrown due to access violation.

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Xaron

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Posted: 29th Jul 2020 08:21

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There seems to be a problem using a map or unordered_map directly it seems.

Just declare it like that in the header:

+ Code Snippet

std::unique_ptr<std::unordered_map<const char*, int>> _test;

And then create it properly in the cpp:

+ Code Snippet

_test = std::make_unique<std::unordered_map<const char*, int>>();
_test->insert(std::pair<const char*, int>("Hello", 10));

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nickydemon

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Posted: 29th Jul 2020 09:21

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Hi Xaron, it works now! Thank you for the solution.
But may I know what's the cause of the problem behind this? It worked fine if I use the other library though..

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Xaron

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Posted: 29th Jul 2020 09:53

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I have no idea actually. It could be that the map isn't properly initialized yet, but I don't know why that should happen there. Maybe due to static linking to the agk lib and weird internal order of initialization? Don't know.

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nickydemon

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Posted: 29th Jul 2020 10:02

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I see. I guess I will just use the solution you provided.

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Paul Johnston

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Posted: 29th Jul 2020 14:57

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It is probably the "memset ( this, 0, sizeof(app));" line, this is setting all the private variables to 0, including the internal variables in the unordered_map. It was originally intended to initialize basic types to 0, but is probably not a good idea when using more complicated types.

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basjak

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Posted: 1st Aug 2020 03:09 Edited at: 1st Aug 2020 03:47

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it obviously the memset. you need to remember that you can't set the 'this' with memset because the object heap access is compiler protected. the 'this' can only be set by accessing its variables and only be deleted either automatically if it is on the stack or through the pointer delete if it is on the heap.

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AppGameKit Studio Chat / TIER 2 : Inserting a new element into unordered_map or map give access violation error

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