std::vector as raw array

Question

Is it safe to get address of first element in std::vector and use it like raw array? Is data aligned continously? What c++ standard says (c++98 vs c++11)? Is it a common practice by the way?

I have some array which size may vary and function which takes pointer and number of elements as argument. It would be great to manage data with std::vector and use it with my_func at same time.

std::vector<int> my_vector;
void my_func(int* int_ptr, int num_ints);
// ..
my_func(&my_vector[0], my_vector.size());

Bathsheba · Accepted Answer · 2014-03-13T12:34:40.197

7

C++11 (and C++03 for that matter) guarantees that the data in std::vector are contiguous. This means, that in your case, &my_vector[0] can be thought of as the pointer to the zeroth element of that array and normal pointer arithmetic can be used to access the other elements. It's preferred to use my_vector.data() to recover the pointer to the zeroth element.

C++98 almost guarantees it.

Note that it's not true for std::vector<bool> for any of the C++ standards. This is because std::vector<bool> is implemented as a particular specialisation.

edited Mar 13 '14 at 12:34

answered Mar 13 '14 at 12:27

Bathsheba

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"almost"? Can you add a quote? – Kiril Kirov Mar 13 '14 at 12:27
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To fill in the blank, C++03 changed it to be guaranteed from C++98. – chris Mar 13 '14 at 12:28
could you link the reference? :) – Theolodis Mar 13 '14 at 12:28
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In c++11, use the much cleaner `data()` member, that syntax is horrid.. :) – Nim Mar 13 '14 at 12:29
@Theolodis: the link is in the dupe – Bathsheba Mar 13 '14 at 12:31
@Nim: I've added to the answer. – Bathsheba Mar 13 '14 at 12:32
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@Bathsheba almost? what does that mean? – Ivars Mar 13 '14 at 12:33
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Don't add to this answer - the question is a duplicate. Post an answer on the original question if you feel you can add to its existing answers. – Lightness Races in Orbit Mar 13 '14 at 12:35

std::vector as raw array

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