Question

I have a class and in there I have a struct which contains a string. In main I declare the class, then create a struct to reach that string.
How it looks like:

Class *myClass = new Class;
Class::Struct *myStruct;

myStruct = &myClass->getStruct(); // the struct is in a vector so I get it through a function

cout << myStruct->string << "\n";

So, with this method I can’t reach the string in the struct, but I can the int’s, float’s, etc.
If I change the code to this:

Class::Struct myStruct;

myStruct = myClass->getStruct();

cout << myStruct.string << "\n";

then it works.

My question is, why is the second one working, and the first not, and why only the string?
It’s not about life and death, because I don’t really need that string, I just tested the program, but I’m really curious what’s going on, because I’m still learning the language, and especially pointers.

Thanks in advance!

EDIT:
Ok, so the definitions

class Class {
public:
    struct Struct {
        string name;
        float data;
    };

    Class();
    Struct getStruct( int i );

private:
    vector<Struct>  tempStruct;
};

Class::Class() {
    Struct str;
    str.name = "test";
    str.data = 1.0f;

    tempStruct.push_back( str );
}

struct Class::getStruct( int i ) {
    return tempStruct[i];
}

EDIT2:
That was a little mistake, but I forgot the &. But you helped me to find it.

Answer 1

This is because getStruct() returns a copy of the struct. This is called a “temporary”. The temporary dies immediately. So now you have a pointer to a dead temporary. It doesn’t exist anymore so the pointer to it is invalid. Either return a pointer or reference to the struct in getStruct(), or hold a reference to its return value like this:

const Class::Struct& myStruct = myClass->getStruct();