how to get the size of an STL container object?!!!

Hi guyz..
I just wanna ask about the size allocated for the objects instantiated from a class container in the STL, for example when I write :

Code:

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cout<<sizeof(list<int>);

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I get the result 24, or when i write:

Code:

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cout<<sizeof(vector<int>);

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I get the result 20, whatever the type of the vector or the list (or any other containers) is set : int , char, double …. I will always get the same.. why!!!
So if I wanna actually know the size of my STL container object .. how would I get it?!!

Use the .size() method.

sizeof() just tells you how many bytes the "head" data structure contains.

The containers allocate memory internally in a dynamic fashion with pointers and calls to new/delete. When you use sizeof on a container, you do not get the size of the memory that has been allocated via these processes, just the memory of any pointers, and miscellaneous data members the container directly "owns". To get the number of bytes the container is managing it would be whatever the size() function returns (number of objects being stored) multiplied by the size of the object stored within the container (more accurately it would likely be capacity() multiplied by the sizeof the stored objects). That plus the sizeof of the container itself would get the total memory footprint occupied by a particular instance of a container (in two [at least] separate memory locations).

Also keep in mind that the total amount of memory used by the container could well exceed that amount, due to other ancillary data (such as inter-nodal pointers). The bottom line is that it varies with implementations.

hi hk_mp5kpdw , thanks for your attention..
i tried what you told me exactly(capacity() multiplied by the sizeof the stored objects) but unfortunately that didn't work
cuz when i wanna get the size of an object from the class vector... i still have the same result , which is 20(per element), whatever the set type is. that is whether the type set is : char , integer ,....etc they are the same :20 one element, 40 two elements , 60 three elements.... and so on!!!!

Quote:

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Originally Posted by sam-j89

cuz when i wanna get the size of an object from the class vector...

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Size of an object in the vector? Or the total size of the vector plus the contents?

Quote:

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Originally Posted by sam-j89

i tried what you told me exactly(capacity() multiplied by the sizeof the stored objects) but unfortunately that didn't work

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Plus the sizeof the container itself. And that's only a general guideline. Containers of containers or objects which themselves manage memory make things difficult.

Code:

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std::vector<int> intVect;
std::cout << "Empty    : " << sizeof(intVect) + sizeof(int) * intVect.capacity() << std::endl;

intVect.push_back(20);
std::cout << "1 Element: " << sizeof(intVect) + sizeof(int) * intVect.capacity() << std::endl;

intVect.push_back(30);
std::cout << "2 Element: " << sizeof(intVect) + sizeof(int) * intVect.capacity() << std::endl;

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Code:

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Empty    : 20
1 Element: 24
2 Element: 28

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Which equates to 20 bytes for the vector<int> itself plus 4 bytes for each int stored within.

What are you ACTUALLY trying to do? In other words, why do you think it makes sense to know the size of the contents of a vector or list container?

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Mats

mmmm i see.. now i got it
thank you so much bro hk_mp5kpdw