std::valarray<T>::begin - cppreference.com

From cppreference.com

	(1)	(since C++11)
const_iterator begin() const;	(2)	(since C++11)

Returns an iterator referring to the first element in the numeric array.

The iterator returned from this function is invalidated when the member function resize() is called on v or when the lifetime of v ends, whichever comes first.

Parameters

Return value

Iterator to the first element in the numeric array.

Exceptions

May throw implementation-defined exceptions.

Notes

Unlike other functions that take std::valarray arguments, begin() cannot accept the replacement types (such as the types produced by expression templates) that may be returned from expressions involving valarrays: (v1 + v2).begin() is not portable, std::valarray<T>(v1 + v2).begin() has to be used instead.

The intent of this function is to allow range for loops to work with valarrays, not to provide container semantics.

Example

#include <algorithm>
#include <iostream>
#include <valarray>

void show(const std::valarray<int>& v)
{
    std::for_each(v.begin(), v.end(), [](int c)
    {
        std::cout << c << ' ';
    });
    std::cout << '\n';
};

int main()
{
    const std::valarray<int> x{47, 70, 37, 52, 90, 23, 17, 33, 22, 16, 21, 4};
    const std::valarray<int> y{25, 31, 71, 56, 21, 21, 15, 34, 21, 27, 12, 6};

    show(x); 
    show(y); 

    const std::valarray<int> z{x + y};

    for (char c : z)
        std::cout << c;
}

Output:

47 70 37 52 90 23 17 33 22 16 21 4 
25 31 71 56 21 21 15 34 21 27 12 6 
Hello, C++!

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2058	C++11	1. `begin()` was required to support replacement types 2. it was unspecified when the returned iterators will be invalidated	1. not required 2. specified
P3016R6	C++11	non-member `begin()` functions introduced inconsistency in range access	changed `begin()` to member functions