C++ Am I adding and accessing my Vector correctly?

Question

I am creating an object and adding it to a std::vector and then later on accessing the std::vector to use member variables from the objects I place in it.

.h that contains the std::vector

std::vector<Field *> vFields;
inline std::vector<Field *> getFields() { return vFields; };

In the .cpp I do this:

Field* f1 = Field::createWithLocation(ccp( p.x, p.y));
addChild(f1->getFieldSprite(), 2);
getFields().push_back(f1); // add the new field to a container
//vFields.push_back(f1); // add the new field to a container

std::cout << "add - # of Fields: " << getFields().size() << std::endl;

When instantiating the Field* f1 above this is happening:

Field* Field::createWithLocation(cocos2d::CCPoint p)
{
    Field* f = new Field();
    //f->autorelease();
    f->initWithLocation(p);
    return f;
}

void Field::initWithLocation(cocos2d::CCPoint p)
{
    setFieldCenterPoint(p);
    setFieldGraphicName(FIELD::fieldIconFileName);

    setFieldSprite(cocos2d::CCSprite::create(getFieldGraphicName().c_str()));
     getFieldSprite()->setPosition(ccp(getFieldCenterPoint().x, getFieldCenterPoint().y));

    setFieldSize(getFieldSprite()->getContentSize());

    setFieldNumber(7159);

    setFieldTag(7159);

    std::cout << "When Field Created #: " << getFieldTag() << std::endl;
}

This works fine and when the Field object is created the std::vector says 1 in size() and the getFieldTag() returns 7159 like it was set.

The problem is when I go to access the Field from the vector something happens and I crash. I found that if I output getTagNumber() it is way different.

Example of accessing the vector:

else if (getFieldLayerState() == kActive)
{
    // so did they click on a field?
    std::cout << "Field Layer Status Is Active" << std::endl;
    std::cout << "touch - # of Fields: " << vFields.size() << std::endl;

    // Loop through the field vector and get the size of each field and see if it was tapped    
    for (int f=0; f<vFields.size(); f++)
    {
        //field = (Field*) getFields().at(f);
        Field* field = (Field*) vFields.at(f);

        std::cout << "field #: "<< field->getFieldNumber() << std::endl;
        std::cout << "field tag: "<< field->getFieldTag() << std::endl;

        if (field->getFieldSprite()->boundingBox().containsPoint(location))
        {
            std::cout << "touched field #: "<< field->getFieldNumber() << std::endl;
            std::cout << "touched field tag: "<< field->getFieldTag() << std::endl;
            _dir->Instance()->getAudioEngine()->playBackgroundMusic("tap.mp3", false);    
        }
     }
}

Sample Output from the cout statements:

When Field Created #: 7159
add - # of Fields: 1
Field Layer Status Is Active

touch - # of Fields: 1
field #: 1769234804
field tag: 353394533`

I crash at the if (field->getFieldSprite()->boundingBox().containsPoint(location)) line above with an EXEC_BAD_ACCESS and it is clear that what is in the vector has changed from what I put in it, or so it seems.

Can anyone help me understand what I am doing wrong?

Answer 1

Your getFields function returns a copy of the vector. So any changes to the returned vector will only happen in the copy, and not the original.

You want to return a reference .

std::vector<Field*>& getFields() { return vFields; }
//                 ^
// Note the ampersand

You might also want to add a const overload of the function as well:

const std::vector<Field*>& getFields() const { return vFields; }
// ^                                      ^
// Note the two `const` modifiers, the last one is important

Then if you modify the vector, eg by adding to it, the compiler will select the first non-const overload. And if you don't modify the vector, eg when you just call size on the vector, the compiler will select the second const overload.