Box2d C++访问冲突使用b2fixture超出方法

Box2d C++ AccessViolation using b2fixture out of method

本文关键字：方法 b2fixture C++ 访问冲突 Box2d      更新时间：2023-10-16

在创建box2d多边形时，我想在将夹具连接到主体的方法之外创建夹具，但当我这样做时，我会遇到访问冲突。

我已经遍历了代码，box2d肯定得到了fixture对象。

当我把夹具连接到身体内部的方法，它工作得很好。当我尝试调用方法时，它会抛出访问违规错误

    b2FixtureDef* LineSegment::GenerateFixture(b2Vec2 vertices[4],b2Body* body,b2World* world){
    b2BodyDef bodyDef;
    //bodyDef.type = b2_kinematicBody;
    bodyDef.position.Set(_currentStepStartPosition.x,_currentStepStartPosition.y);
    body =world->CreateBody(&bodyDef);
    int32 count = 4;
    b2PolygonShape polygon;
    polygon.Set(vertices, count);
    b2FixtureDef fixtureDef2;
    fixtureDef2.shape = &polygon;
    fixtureDef2.density = 1.0f;
    fixtureDef2.friction = 0.3f;
    body->CreateFixture(&fixtureDef2);/// works if i attatch the fixture here here
    return &fixtureDef2;
}

调用方法，当我把固定装置连接到时失败

    bool LineSegment::GenerateNextBody(b2Body* retBody){
    b2BodyDef bodyDef;
    bodyDef.type = b2_staticBody;
    bodyDef.position.Set(_currentStepStartPosition.x,_currentStepStartPosition.y);
    retBody =world->CreateBody(&bodyDef);
    _currentStep++;
    b2Vec2 vertices[4];
    if(_inclinePerStep != 0){
    GetVertsInclineSquare(vertices,_stepWidth,_thickness,_inclinePerStep);
    }else{
        GetVertsSquare(vertices,_stepWidth,_thickness);
    }
    if(_currentStep == 1){
        _GameWorldVerticies[0] =b2Vec2((_currentStepStartPosition.x+vertices[0].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[0].y)*PTM_RATIO);
        _GameWorldVerticies[3] =b2Vec2((_currentStepStartPosition.x+vertices[3].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[3].y)*PTM_RATIO);
    }
    b2FixtureDef* fixture = GenerateFixture(vertices,retBody,world);
    //retBody->CreateFixture(fixture); throws a access violation if i attatch the fixture here
    _currentStepStartPosition.x += vertices[2].x+(vertices[2].x);
    _currentStepStartPosition.y +=(_inclinePerStep/2);
    if(_steps <= _currentStep){
        _GameWorldVerticies[1] =b2Vec2((_currentStepStartPosition.x+vertices[1].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[1].y)*PTM_RATIO);
        _GameWorldVerticies[2] =b2Vec2((_currentStepStartPosition.x+vertices[2].x)*PTM_RATIO,(_currentStepStartPosition.y+vertices[2].y)*PTM_RATIO);
        return false;
    }
    return true;
}

更新

新代码段

        b2FixtureDef* fixtureDef2 = new b2FixtureDef();
    fixtureDef2->shape = &polygon;
    fixtureDef2->density = 1.0f;
    fixtureDef2->friction = 0.3f;
    //body->CreateFixture(&fixtureDef2);/// works if i attatch the fixture here here
    return fixtureDef2;

问题是返回一个指向GenerateFixture中局部变量的指针，这是未定义的行为。变量fixtureDef2在堆栈上，当函数返回时，堆栈的该区域不再有效。当您延迟调用CreateFixture函数时，指针现在将指向该函数的堆栈区域。

为了解决这个问题，您可以在堆上创建它，例如new。

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