list size

[para1131]

why can not get sizeof of a list? Is it like Type *array; that you can not get the size of array and just return the size of pointer which point ro first element of array?

sizeof return 16 for both sizeof(C1/2)=16 and sizeof(char)=1 ,sizeof(char)=8.why sizeof for any list type return 16byte?

inorder to get size of a list i should multiply list.size by sizeof(list type)???

std::list<char*> C1;
std::list<char> C2;

cout<<sizeof(C1)<<endl;
cout<<sizeof(C2)<<endl;

Thanks

[Peter87]

std::list probably contains two pointers, one to the first node and one to the last node. If the size of a pointer is 8 bytes that adds up to 16 bytes. In C++11 it would also have to keep track of the number of elements so if you compile the code in C++11 it would probably give you a size of 24 bytes.

If you want to get the number of elements stored in the list you can use the size member function.
http://en.cppreference.com/w/cpp/container/list/size

[rmxhaha]

Why 16 byte ?
I don't really know but this is the STL source code

template <class _Tp>
struct _List_node {
  typedef void* _Void_pointer;
  _Void_pointer _M_next;
  _Void_pointer _M_prev;
  _Tp _M_data;
};

So I think this struct must be 16 byte in some cases
It's a template. You can't just generelized the size. It changes based on your type

Yes, I think it's the only way I can think of
int q = C1.size() * sizeof( char*);


I don't think I ever need to find out about the size of a list...
Well, that's my case
yours must be different

I am sorry if I gave you the wrong answers

[S G H]

Peter87, on 32-bits, the size of a pointer is 4 bytes. Being there 4 pointers (suppose a pointer-sized _M_data variable) the size of the struct is 16 byte, because you are getting the list's size, not the content's size.

[Peter87]

The code that rmxhaha posted is for the nodes. The size of a node will be different for different types.

[rmxhaha]

Correct me if I am wrong
From looking at STL List

class list is inhereited from a class named _List_Base
Which only have 1 member

_List_node<_Tp>* _M_node;

It's really is hard reading trough the source code
I don't think I can help you
I am sorry

[LB]

It is hard to read through the source code of the STL because you're not supposed to do it. The problem here is that the OP is seeing implementation-defined behavior.

[ne555]

> because you're not supposed to do it. (read STL source code)
¿why not?


@OP: iirc sizeof is computed at compile time

[Cubbi]

There's nothing wrong looking at the C++ library headers (or even sources), just keep in mind that every implementation is different. Personally, I like LLVM libc++ code best: http://llvm.org/svn/llvm-project/libcxx/trunk/include/list