Violation d'accès! comment ne plus avoir cette erreur!

Bonjour:D !!

J’ai souvent atterri ici depuis que j'ai commencé à travailler avec le builder c++ ça fait de cela 1 mois, pour des opérations élémentaires. Et j'ai toujours était satisfait ! Cependant, cette fois-ci le problème semble être plus coriace!

Alors voilà, je travail avec l’algorithme de pathfinder (j’utilise A*) dans une application de robot. Je donne le point de départ, et le point d’arrivée, je clique sur le bouton, le programme se lance, et j’ai mon meilleur chemin ! Cependant, dés que je choisi un autre point de départ et d’arrivée, j’ai une erreur de type :

« Project1.exe a provoqué une classe d’exception EAccessViolation avec le message ‘Violation d’accès à l’adresse 004038A5 dans le module ‘Project.exe’. Ecriture de l’adresse 00000018… »8O :help:

Qu’est ce que cela veut dire au juste ? Et qu’est ce que je dois faire pour ne plus avoir cette erreur ?

Sachez que si je change mon point de départ et d’arrivée 1 case par 1 case (sans que je le fasse avancer de deux cases par exemple) cette erreur n’apparaît plus…c’est très étrange !

Merci d’avance pour votre aide :P !

Cela correspond à une erreur de ton programme (mauvaise utilisation d'un pointeur, débordement d'une zone mémoire ...).

Seule une lecture attentive de ton code (et éventuellement un ajout de traces) te permettra de déterminer la cause de l'erreur.

Si ce code n'est pas trop long, poste le ici ...

bonjour! merci pour ta réponse! en fait, ça m'étonnerai que je pourrai poster tout mon programme ici. il contient plus de 1000 lignes! voilà le bout de code qui me fait ce problème:

Code:

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void writePathToGrid() { if( currentState == SUCCEEDED ) { //Iterate back to the startNode from the endNode Node *nodeChild = endNode; Node *nodeParent = endNode->parent; do { if( nodeParent != startNode ) { nodeParent -> type = pathTile; // l'erreur se situe à ce niveau grid[nodeParent->x][nodeParent->y] = pathTile; } nodeChild = nodeParent; nodeParent = nodeParent->parent; } while( nodeChild != startNode ); } return; }

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je ne sais pas si cela pourrai vous aider à trouver le problème!

Merci encore.

Je ne connais pas ton code, mais je te conseillerais de faire un peu de validation, par exemple:

Code:

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void writePathToGrid() { if( currentState == SUCCEEDED ) { //Iterate back to the startNode from the endNode Node *nodeChild = endNode; Node *nodeParent = endNode->parent; if(nodeChild && nodeParent) { do { if( nodeParent != startNode ) { nodeParent -> type = pathTile; // l'erreur se situe à ce niveau grid[nodeParent->x][nodeParent->y] = pathTile; } nodeChild = nodeParent; nodeParent = nodeParent->parent; } while( nodeChild != startNode ); } } return; }

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Tu pourrais valider startNode et pathTile avant de les utiliser. Étant donné qu'ils ont l'air d'être des variables globales je ne sais pas comment les valider. Il faudrais que je connaisse le type de variable.

Bonsoir,
Tu peux aussi utiliser l'outil Code Guard pour t'aider à trouver l'origine de ton problème.
Vas dans 'Projet', 'Options...' puis l'onglet 'CodeGuard'.
Cliques sur 'CodeGuard Violation' et sélectionnes toutes les options disponnibles.
Faits un Build complet de ton programme, puis un Make. Enfin exécutes letout, et avec un peu de chance tu auras des informations un peu plus précisent sur l'origine de ta violation d'accés.
Bon courage et bonne chance.
Cordialement,
Benjamin

Bonjour ! Je m’excuse pour le retard ! C’est vraiment gentil de votre part, ça m’a permit d’éclairer un peu mes idées ! Cependant, je n’ai toujours pas réussi à trouver la source du problème étant donné que la programmation ce n’est pas vraiment mon point fort. Alors, je vais vous poster un autre bout de code peut-être que vous arriveriez à trouver l’origine du problème

Code:

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#define GRID_SIZE 61 #define TS 10 int grid[GRID_SIZE][GRID_SIZE];   // Function Prototypes void renderGrid(); void setSE(); void makeGrid(); void resetGrid();   enum { wallTile, openTile, startTile, endTile, pathTile, };   //-------------------------------------- Class Declaration and Instantiation class Astar { public: // Public Member Variables enum { SEARCHING, SUCCEEDED, FAILED, };   // Node class (class that has x, y, heuristic and parent pointer values class Node { public: Node() { parent = NULL;   g = 0.0; h = 0.0; f = 0.0; }   /*****getDistanceEstimate()*****                 *TAKES: int endx:       x value of the endNode                 *       int endy:       y value of the endNode                 *RETURNS: float:        the value of the distance equation squared                 *PURPOSE: to calculate and return the distance from this                 *node to the endNode                 ********************************/ float getDistanceEstimate( int endx, int endy ) { float dx = (float)( (float)x - (float)endx ); float dy = (float)( (float)y - (float)endy );   return ((dx*dx) + (dy*dy));     }   /*****isSameState()*****                 *TAKES: Node *rhs:      node to check x,y values                 *RETURNS: bool:         is this the same state?                 *PURPOSE: true if the passed node has the same                 *x and y values as this node                 ************************/ bool isSameState( Node *rhs ) { if( x == rhs -> x && y == rhs -> y ) return true; else return false; }     Node *parent;   float g; // cost of this node + its parents float h; // heuristic estimate float f; // g + h   int x, y; int type; };   class HeapComparison { public:   /*****operator()*****                 *TAKES: Node *x:        first node for comparison                 *       Node *y:        second node for comparison                 *RETURNS: bool:         does x have higher f than y?                 *PURPOSE: this function is passed to the list sorting                 *functions, pop_heap, push_heap, and sort_heap                 *this function dictates the order of the list                 *the heap functions are an A* optimization                 *********************/ bool operator() ( const Node *x, const Node *y ) const { return x->f > y->f; } };   //---------------------------------------------------------- Member Functions   Astar() { // Constructor }     ~Astar() { // Destructor clearLists(); }   //Reset function void clearLists() { OPEN.clear(); CLOSED.clear(); SUCCESSORS.clear(); }   /*****getCoords()*****         *TAKES: int xCoord:     x coordinate for the desired grid value         *               int yCoord: y coordinate for the desired grid value         *RETURNS: int:          the tile value of grid[x][y]         *PURPOSE: to return the tile value at coordinates xCoord, yCoord         *Values that are out of bounds (bigger than size of grid)         ************************/ int getCoords( int xCoord, int yCoord ) { if( xCoord < 0 || xCoord >= GRID_SIZE || yCoord < 0 || yCoord >= GRID_SIZE ) return wallTile;   return grid[xCoord][yCoord]; }     /*****setStartEnd()*****         *TAKES: int x:  x value of startNode         *               int y:  y value of startNode         *               int q:  x value of endNode         *               int r:  y value of endNode         *RETURNS: nothing         *PURPOSE: initializes the startNode and endNode         ************************/ void setStartEnd( int x, int y, int q, int r) { startNode = new Node; endNode = new Node;   //Initialize the start and ending nodes startNode -> x = x; startNode -> y = y; startNode -> type = startTile; endNode -> x = q; endNode -> y = r; endNode -> type = endTile;   //Set state of the search algorithm currentState = SEARCHING;   //Initialize the heuristic variables for the start state startNode->g = 0; startNode->h = startNode->getDistanceEstimate( endNode -> x, endNode ->y ); startNode->f = startNode->g + startNode->h; //Starting node has no parents startNode->parent = NULL;   //Push starting node onto OPEN list OPEN.push_back( startNode );   // Sort elements in heap push_heap( OPEN.begin(), OPEN.end(), HeapComparison() );   // Initialise counter for search steps stepCounter = 0;   }     /*****Search()*****         *TAKES: nothing         *RETURNS: unsigned int: corresponds to a particular state         *                       SUCCEEDED:      found the endNode         *                       FAILED:         didn't find the endNode         *                       SEARCHING:      still searching, keep calling trying         *PURPOSE: A* algorithm.  Starts at the lowest f valued node on         *the OPEN list (first iteration is always the startNode) and         *stores it as thisNode.  The OPEN list contains every node that         *hasn't been expanded, ie. has not had successors generated for         *it The CLOSED list contains every node that has been expanded,         *Search() then generates all the 0 to 8 successors of thisNode         *and iterates through them.  Any successor that is found to meet         *both of the following conditions is placed in the OPEN list         *and it's parent node is stored.         *               1) If this successor is already a node on the OPEN list, and         *                       the 'f' value of the node on the OPEN list is higher         *                       than that of the successor.  Consequentially, this         *                       successor was reached faster (from a different direction)         *                       than it was when it was first put on the OPEN list.         *                       This successor must be updated on the OPEN list with         *                       the lower 'f' value.         *               2) If this successor is already a node on the CLOSED list, and         *                       the 'f' value of the node on the CLOSED list is higher         *                       than that of the successor.  Consequentially, this         *                       successor was reached faster (from a different direction)         *                       than it was when it was first put on the CLOSED list.         *                       Because this successor has already been expanded (it         *                       is on the CLOSED list) and has a lower 'f' value         *                       than its similar state on the CLOSED list, this         *                       successor must be removed from the CLOSED list.         *                       If this successor meets both criteria, it will be         *                       placed on the OPEN list and expanded again.         *If this successor is neither on the OPEN nor on the CLOSED lists, it         *will be put on the OPEN list and have it's parent node stored.  After         *Search() has stored every worthwhile successor (those that have met         *the two criteria), it will move the successors' parent onto the CLOSED         *list.  Search should then be called again, where it will expand the Node         *on the OPEN list with the lowest 'f' value.  If a node taken off the OPEN         *list is the endNode, Search() will set the currentState flag to SUCCEEDED         *and terminate the subroutine.  If the OPEN list is empty, there are no         *more states to expand, and therefore no way to get to the endNode.         *******************/ unsigned int Search() { //Check to see if the search succeeded or failed if( ( currentState == SUCCEEDED) || ( currentState == FAILED ) ) return currentState;   //The search fails if the OPEN list is empty (no more states to search) if( OPEN.empty() ) { currentState = FAILED; return currentState; }   // Incremement stepCounter stepCounter ++;   //Get the node with the lowest f value (list is always sorted in order //of f values) Node *thisNode = OPEN.front(); pop_heap( OPEN.begin(), OPEN.end(), HeapComparison() ); OPEN.pop_back();   // Check for the end state if( thisNode -> type == endTile ) { //Store the parent of end node so we can move back up the tree endNode->parent = thisNode->parent;   //Make sure startNode isn't equal to endNode if( thisNode != startNode ) { //delete thisNode; delete thisNode;   }   currentState = SUCCEEDED;   return currentState; } //End state not found else {   //Generate successors for the node in question //Start by clearing the successor list of the last "thisNode" SUCCESSORS.clear();   //Push successors of thisNode into SUCCESSORS list.   Node * newNode; //Store x and y coords of thisNode's parent so it doesn't go backwards //Make a case for the startNode (it has no parent) int parentX = -1; int parentY = -1;   //Check to see that thisNode has a parent (ie, its not the start node) if( thisNode -> parent ) { parentX = thisNode -> parent -> x; parentY = thisNode -> parent -> y; }   //Create successor by scanning around thisNode's x,y coords //Case: Left of thisNode if( (getCoords( (thisNode -> x)-1, (thisNode -> y) ) != wallTile) && !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y))) ) { newNode = new Node;   newNode -> x = (thisNode -> x)-1; newNode -> y = thisNode -> y; newNode -> type = getCoords( (thisNode -> x)-1, (thisNode -> y) );   SUCCESSORS.push_back( newNode ); }   //Case: Right of thisNode if( (getCoords( (thisNode -> x)+1, (thisNode -> y) ) != wallTile) && !((parentX == (thisNode -> x)+1) && (parentY == (thisNode -> y))) ) { newNode = new Node;   newNode -> x = (thisNode -> x)+1; newNode -> y = thisNode -> y; newNode -> type = getCoords( (thisNode -> x)+1, (thisNode -> y) );   SUCCESSORS.push_back( newNode ); }   //Case: Upper Left of thisNode if( (getCoords( (thisNode -> x)-1, (thisNode -> y)-1 ) != wallTile) && !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y)-1)) ) { newNode = new Node;   newNode -> x = (thisNode -> x)-1; newNode -> y = (thisNode -> y)-1; newNode -> type = getCoords( (thisNode -> x)-1, (thisNode -> y)-1 );   SUCCESSORS.push_back( newNode ); }   //Case: Above thisNode if( (getCoords( (thisNode -> x), (thisNode -> y)-1 ) != wallTile) && !((parentX == (thisNode -> x)) && (parentY == (thisNode -> y)-1)) ) { newNode = new Node;   newNode -> x = thisNode -> x; newNode -> y = (thisNode -> y)-1; newNode -> type = getCoords( (thisNode -> x), (thisNode -> y)-1 );   SUCCESSORS.push_back( newNode ); }   //Case: Upper Right of thisNode if( (getCoords( (thisNode -> x)+1, (thisNode -> y)-1 ) != wallTile) && !((parentX == (thisNode -> x)+1) && (parentY == (thisNode -> y)-1)) ) { newNode = new Node;   newNode -> x = (thisNode -> x)+1; newNode -> y = (thisNode -> y)-1; newNode -> type = getCoords( (thisNode -> x)+1, (thisNode -> y)-1 );   SUCCESSORS.push_back( newNode ); }   //Case: Lower Left of thisNode if( (getCoords( (thisNode -> x)-1, (thisNode -> y)+1 ) != wallTile) && !((parentX == (thisNode -> x)-1) && (parentY == (thisNode -> y)+1)) ) { newNode = new Node;   newNode -> x = (thisNode -> x)-1; newNode -> y = (thisNode -> y)+1; newNode -> type = getCoords ( (thisNode -> x)-1, (thisNode -> y)+1 );   SUCCESSORS.push_back( newNode ); }   //Case: Below thisNode if( (getCoords( (thisNode -> x), (thisNode -> y)+1 ) != wallTile) && !((parentX == (thisNode -> x)) && (parentY == (thisNode -> y)+1)) ) { newNode = new Node;   newNode -> x = thisNode -> x; newNode -> y = (thisNode -> y)+1; newNode -> type = getCoords( (thisNode -> x), (thisNode -> y)+1 );   SUCCESSORS.push_back( newNode ); }   //Case: Lower Right of thisNode if( (getCoords( (thisNode -> x)+1, (thisNode -> y)+1 ) != wallTile) && !((parentX == (thisNode -> x)+1) && (parentY == (thisNode -> y)+1)) ) { newNode = new Node;   newNode -> x = (thisNode -> x)+1; newNode -> y = (thisNode -> y)+1; newNode -> type = getCoords( (thisNode -> x)+1, (thisNode -> y)+1 );   SUCCESSORS.push_back( newNode ); }       //Iterate through all the successors of thisNode for( vector< Node * >::iterator successor = SUCCESSORS.begin(); successor != SUCCESSORS.end(); successor ++ ) {   //Store the g value for this successor in a temporary variable float newg = thisNode->g + 1.0;   //Check to see if this successor is on the open or closed lists vector< Node * >::iterator openlist;   for( openlist = OPEN.begin(); openlist != OPEN.end(); openlist ++ ) { if( (*openlist)->isSameState( (*successor) ) ) { break; } }   if( openlist != OPEN.end() ) {   //This successor state is on the OPEN list //Now check to see which has the lower g value if( (*openlist) -> g <= newg ) { delete (*successor);   //the one on OPEN is cheaper than this one //so trash this successor and continue continue; } }   vector< Node * >::iterator closedlist;   for( closedlist = CLOSED.begin(); closedlist != CLOSED.end(); closedlist ++ ) { if( (*closedlist) -> isSameState( (*successor) ) ) { break; } }   if( closedlist != CLOSED.end() ) {   //This successor state is on the OPEN list //Now check to see which has the lower g value if( (*closedlist) -> g <= newg ) { //the one on CLOSED is cheaper than this one //so trash this successor and continue delete (*successor);   continue; } }   //This successor is fewer steps (g's value) away from the start //Than any occurance on the open or closed list //save parent so we can back track once (if?) we reach the end (*successor) -> parent = thisNode; //Store our temporary g value (*successor)->g = newg; //find the distance (squared) from this point to the endnode (*successor)->h = (*successor) -> getDistanceEstimate( endNode -> x, endNode -> y ); //Get the final heuristic value f (*successor)->f = (*successor) -> g + (*successor) -> h;   //Remove successor from CLOSED if it was on it and had lower g   if( closedlist != CLOSED.end() ) { //remove this successor from CLOSED so we don't //try to compare it again the next time around delete (*closedlist);   CLOSED.erase( closedlist );   }   //Update old version of this successor node on OPEN list if( openlist != OPEN.end() ) {   delete (*openlist);   OPEN.erase( openlist );   //resort the heap sort_heap( OPEN.begin(), OPEN.end(), HeapComparison() ); }   //Put this successor (with newest values) into the OPEN list OPEN.push_back( (*successor) );   //Sort the OPEN list push_heap( OPEN.begin(), OPEN.end(), HeapComparison() );   }   //Push thisNode onto CLOSED, it has been expanded   CLOSED.push_back( thisNode );   }   //End of the else, //the currentState should only be unsuccessful at this point return currentState;   } //Function that moves from the endNode to the startNode //and changes the path From '.' to 'X'   void writePathToGrid() { if( currentState == SUCCEEDED ) { //Iterate back to the startNode from the endNode Node *nodeChild = endNode; Node *nodeParent = endNode->parent;   do { if( nodeParent != startNode ) { nodeParent -> type = pathTile; grid[nodeParent->x][nodeParent->y] = pathTile; }   nodeChild = nodeParent; nodeParent = nodeParent->parent;   } while( nodeChild != startNode ); } return; }   private:     //OPEN list explained in comments before Search() vector<Node *> OPEN;   //CLOSED list explained in comments before Search() vector<Node *> CLOSED;   //SUCCESSORS is a list of successive nodes branching out from //any particular node. It is generated almost every iteration of SEARCH vector<Node *> SUCCESSORS;   unsigned int currentState;   int stepCounter;   //Start and end state pointers Node *startNode; Node *endNode;   } aStarSearch;

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Apparemment, les variables startNode et pathTile ont l’air d’être des variables globales comme vous dites.
je souhaite vraiment que vous puissiez me trouver la solution. je suis perdu!
Merci encore une fois.
A plus!

Dans les bonnes pratiques, il faut veiller à ce que toutes les variables soient initialisées avant de s'en servir. Mais comme ça fonctionne une fois je ne pense pas que ça vienne de ça.

Deuxièmement, il faut aussi veiller à mettre la valeur NULL dans les pointeurs après un delete ; exemple :

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... delete MonPointeur; MonPointeur = NULL; ...

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Ca évitera de se resservir d'un pointeur désalloué.

Troisièmement, il faut veiller à tester qu'un pointeur n'est pas à NULL avant de s'en servir ; exemple :

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... if (MonPointeur) MonPointeur->MaMethode(); ...

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A priori ton problème ressemble à l'utilisation d'un poiteur désalloué, mais pas remis à NULL. Code Guard devrait t'aider à trouver.