填充指向返回结构的类get函数的指针数组

Question

I'm trying to fill an array of pointers. I need the myVar data of the two (or more) instances of the MyClass. But for some reason I am not getting the results I want.

Header file:

typedef struct {
    int value;
    int otherValue; // We do nothing with otherValue in this example.
} mytype_t;

class MyClass {
    public:
        MyClass(void) {}
        ~MyClass(void) {}
        void set(float _value) {
            myVar.value = _value;
        }
        mytype_t get(void) { // We get the data through this function.
            return myVar;
        }
    protected:
    private:
        mytype_t myVar; // Data is stored here.
};

Cpp file:

MyClass myInstances[2];

int main(void) {

    // Set private member data:
    myInstances[0].set(75); 
    myInstances[1].set(86);

    mytype_t *ptr[2];

    ptr[0] = &(myInstances[0].get());
    ptr[1] = &(myInstances[1].get());

    Serial.print(ptr[0]->value); // Prints 75 -> As expected!
    Serial.print(":");
    Serial.print(ptr[1]->value); // Prints 86
    Serial.print("\t");

    for (int i = 0; i < 2; i++) {
        Serial.print(myInstances[i].get().value); // Prints 75, and next iteration 86 -> As expected.
        if (i == 0) Serial.print(":");
        ptr[i] = &(myInstances[i].get()); // Set ptr
    }
    Serial.print("\t");

    Serial.print(ptr[0]->value); // Prints 86 -> Why not 75..?
    Serial.print(":");
    Serial.print(ptr[1]->value); // Prints 86
    Serial.println();
}

The program outputs:

75:86   75:86   86:86

And not:

75:86   75:86   75:86

Why is it pointing to the other instance (with value 86) instead? And how can I fix it? Or is the thing I want not possible?

PS The code is run on a PC platform. I am using my own Serial class based on the syntax of Arduino.

Answer 1

You are assigning pointers to the temporary objects returned from get . You are not assigning pointers to the internals of your MyClass objects. Change your code so that get returns a reference instead of a copy.

mytype_t& get(void) { // We get the data through this function.
        return myVar;
}

That should make your program work. However it's not considered good practise to return a reference to the internals of another object. You should probably reconsider your design.