C++ Template: what does this ... mean?

Asked Aug 27 '16 at 06:08

Active Aug 27 '16 at 06:27

Viewed 40 times

I met a piece of code below and get lost:

template<typename T>
T add(T t, T u)
{
    return t + u;
}

template<typename ... T>
std::vector<int> add_values(int value, T ... t)
{
    return{ add(t, value)... }; //what does this ... mean?
} 

int main()
{
    add_values(4); 

    return 0;
}

I can understand that the typename ... T means a series of types, and T ... t means a series of T1 t1, T2 t2 .... parameters. But what does the ... in the return{ add(t, value)... } line mean?

asked Aug 27 '16 at 06:08

athos

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2

Look for "variadic template" and parameter pack expansion – KIIV Aug 27 '16 at 06:09
1

It means `return { add(t1, value), add(t2, value), ...};` just as you'd expect. – Barmar Aug 27 '16 at 06:12
@Barmar hmmm... so what is the data type of `{ add(t1, value), add(t2, value), ...}` ? this is not a `std::vector` right? – athos Aug 27 '16 at 06:14
Yes, it's a `std::vector`, since that's the return type of your function. – Barmar Aug 27 '16 at 06:16
@Barmar OK, let me check it out. – athos Aug 27 '16 at 06:18
1

It's initializer_list used for returned vector constructor – KIIV Aug 27 '16 at 06:18
@KIIV thank you, let me google that. – athos Aug 27 '16 at 06:19

C++ Template: what does this ... mean?

0 Answers0