variable scope question

[stampede]

The difference is that first line is declaration of a pointer, visible only in current method, that is constructor. The recordNumberSpinBox member variable is not initialized, so you have a crash when trying to access it. If you want to use the spinbox in other methods, you should leave the declaration in the header, and initialize the member variable:

this->recordNumberSpinBox = new QSpinBox();

this->recordNumberSpinBox = new QSpinBox();

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Consider this example, it's just like your issue:

class A{
protected:
    int var; //member variable, every object of class A has its own var
public:
    A(){
        this->var = 10; // initializes this object member variable with value 10
        int var = 1; // creates local variable named var, visible only in this constructor
        std::cout << "var = " << var << ", this->var = " << this->var << "\n"; 
        // prints: var = 1, this->var = 10
    }
    void method(){
        int x = var + 1; // x = 11, because this objects member variable is used
    }
};

class A{
protected:
    int var; //member variable, every object of class A has its own var
public:
    A(){
        this->var = 10; // initializes this object member variable with value 10
        int var = 1; // creates local variable named var, visible only in this constructor
        std::cout << "var = " << var << ", this->var = " << this->var << "\n"; 
        // prints: var = 1, this->var = 10
    }
    void method(){
        int x = var + 1; // x = 11, because this objects member variable is used
    }
};

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