Question

This code failed at run time and not at compile time. I am not expert in C++.
Any help?

extern void fn();

int main(int argc, char** argv) {
    fn();
}

void fn()
{
    struct Foo{
        string name;
    }*foo;
    foo->name="sleiman";
    cout<<foo->name<<endl;
}

Why does this code fail at run time and why does it succeed if I create a static instance?

void fn()
{
    struct Foo{
        string name;
    }foo;
    foo.name="sleiman";
    cout<<foo.name<<endl;
}

Answer 1

foo is made to be a pointer but is not initialised so when you try to access name it is reading invalid memory. You initialise foo as a pointer to a Foo struct but do not tell it to point to an actual object so is in effect a loose pointer.

In order to make this work you will need to make the pointer point to an actual object by using the new keyword or some other means.