cocos2d-x 3.1 EXC_BAD_ACCESS on Touch event + function - cocos2d-x

Question

I'm cocos2d-x beginner and having trouble with TouchBegan event + function.
I always get EXC_BAD_ACCESS in the [label->setString("Foo Bar");] point when I run this simple code with xCode(5.1.1 + iPhone sim 7.1).
I tried a few ways to solve, but I'm completely stuck up in this problem for 2 or 3 days.
Does anyone have any idea for the wrong point?
HelloWorld.h
#ifndef __HELLOWORLD_SCENE_H__
#define __HELLOWORLD_SCENE_H__
#include "cocos2d.h"
class HelloWorld : public cocos2d::LayerGradient
{
public:
static cocos2d::Scene* createScene();
virtual bool init();
bool onTouchBegan(cocos2d::Touch* touch, cocos2d::Event* event);
cocos2d::Label* label;
CREATE_FUNC(HelloWorld);
};
#endif // __HELLOWORLD_SCENE_H__
HelloWorld.cpp
#include "HelloWorldScene.h"
USING_NS_CC;
Scene* HelloWorld::createScene()
{
auto scene = Scene::create();
auto layer = HelloWorld::create();
scene->addChild(layer);
return scene;
}
bool HelloWorld::init()
{
if(!LayerGradient::initWithColor(Color4B(0, 0, 0, 255), Color4B(50, 50, 50, 255))){
return false;
}
Size visibleSize = Director::getInstance()->getVisibleSize();
Vec2 origin = Director::getInstance()->getVisibleOrigin();
auto label = Label::create("Hello World", "Arial", 112);
label->setPosition(Vec2(origin.x + visibleSize.width/2,
origin.y + visibleSize.height - label->getContentSize().height));
this->addChild(label, 1);
auto listener = EventListenerTouchOneByOne::create();
listener->setSwallowTouches(true);
listener->onTouchBegan = CC_CALLBACK_2(HelloWorld::onTouchBegan, this);
this->getEventDispatcher()->addEventListenerWithFixedPriority(listener, 100);
return true;
}
bool HelloWorld::onTouchBegan(Touch *touch, Event *event){
label->setString("Foo Bar");
return true;
}
Thank you.

Answer 1

Your problem is in this line :
auto label = Label::create("Hello World", "Arial", 112);
In this line you declare a new variable named label whose scope is only for the init function. You also have a class variable also named label and they're not the same. If you declare a variable in a method with the same name as a class variable, it will shadow it. Consider this example :
class A {
int variable;
void method() {
int variable; // this is not the same thing as the one above
variable = 5; //assignment to local variable
this->variable = 3; //asignment to class variable
}
}
So you actually don't assign anything to your class variable label which you later reference in the touch method. The easiest way to solve this would be to remove the auto keyword at auto label from your init() method.

Answer 2

As noted by #Losiowaty, the use of auto can be dangerous sometimes.
cocos2d::Label* label = cocos2d::Label::create("Hello World", "Arial", 112);
Also, there might be a better constructor to use: http://www.cocos2d-x.org/reference/native-cpp/V3.1rc0/db/de4/classcocos2d_1_1_label.html