std::array error: Has no member named 'assign'

Question

In the following code, the compiler complains as: struct std::array<double,5ul> has no member named 'assign' . Here , it seems possible. Why is it so? (Compiler: g++ 4.8.2)

#include <array>

int main()
{
    std::array<double,5> arr;
    arr.assign(4.); // error: has no member named 'assign'
    return 0;
}

Answer 1

array::assign() is a Visual Studio extension. You are compiling with g++. Check here standard g++ array

Answer 2

As already mentioned, there simply is no assign member to std::array .

The interesting question now becomes why ? After all, the other containers have an assign member method !

I would note that unlike other containers, std::array has a fixed size. If you use std::vector<T>::assign (which would be a close equivalent), the vector is resized appropriately to match the size of the sequence being assigned; with an array, however, that would be impossible:

• what would you do if the sequence being assigned is shorter than the array ?
• what would you do if the sequence being assigned is longer than the array ?

this would be counter-intuitive, as the question does not arise for the other containers since their size is just adapted on the fly.

For a similar reason, std::array does not have: reserve , capacity , clear , insert , emplace , erase , push / pop (and variants) or resize . All of them suppose a container which size may vary.

Answer 3

That is very simple, as you can see here there is no assign member function for an std array. There is however a member function called fill you should be able to use.

Answer 4

The assign method it is not a member of std::array . The member fill does what the assign did in TR1.

assign was originally part of std::tr1::array (from the TR1 ) and was changed to be fill circa the C++0x (now C++11) draft n2798 (2008).

This is not really a Microsoft extension, I would imagine that they have probably maintained this method for compatibility with, and support for tr1 implementations in production (the method implementations are exactly the same).