std::vector - error: cannot delete objects that are not pointers - c++

Question

Maybe someone can help me understand the error.
I write this code:
class Text
{
private:
struct paragraph
{
vector<string> lines;
};
vector<shared_ptr<paragraph>> paragraphs;
public:
Text()
{
paragraphs.push_back(shared_ptr<paragraph>(new paragraph()));
}
};
int main()
{
shared_ptr<Text> pText(nullptr);
Text text();
pText.reset(&text);
return 0;
}
When I try to run it
I got this error:
1>c:\program files\microsoft visual studio 10.0\vc\include\memory(1664): error C2541: 'delete' : cannot delete objects that are not pointers
1> c:\program files\microsoft visual studio 10.0\vc\include\memory(1431) : see reference to function template instantiation 'void std::tr1::shared_ptr<_Ty>::_Resetp<_Ux>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
1> c:\program files\microsoft visual studio 10.0\vc\include\memory(1607) : see reference to function template instantiation 'std::tr1::shared_ptr<_Ty>::shared_ptr<_Ux>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
1> c:\documents and settings\owner\שולחן העבודה\e\class.cpp(29) : see reference to function template instantiation 'void std::tr1::shared_ptr<_Ty>::reset<Text(void)>(_Ux (__cdecl *))' being compiled
1> with
1> [
1> _Ty=Text,
1> _Ux=Text (void)
1> ]
What is meant "cannot delete objects that are not pointers"?
I'm not trying to delete any object.

Answer 1

In addition to the most vexing parse, your code contains a fundamental flaw:
You must not assign a pointer to a stack-allocated object to a shared_ptr.
This code will cause undefined behaviour which in practice means lots of pain:
shared_ptr<Text> pText(nullptr);
Text text;
pText.reset(&text);
shared_ptr will try to delete &text at the end of its lifetime.

Answer 2

The line Text text(); does not do what you think it does.
It parses it as the declaration of a function named text which accepts no argument and returns a value of type Text.
This is the reason why your line pText.reset(&text); does not compile.
However, you really do not want that line to compile: you are associating a shared_ptr object to a value with automatic storage duration: when the shared_ptr will go out of scope, it will try to delete that object, resulting in Undefined Behavior (most likely a crash in this case).

Answer 3

You main function should read.
int main()
{
shared_ptr<Text> pText(new Text);
return 0;
}
You had 2 problems. First, Text text() was being parsed as a function declaration. Second, you were passing the address of a stack variable to a shared_ptr, which will delete the object when the reference count reaches 0.
You should also consider whether you need to use a shared_ptr. Will you ever be sharing this pointer with any body else, or do you simply want to ensure it is destructed properly? You could consider unique_ptr in the latter case. Do you even need a pointer at all, could you just allocate the object on the stack?