# std::begin(std::valarray)

From cppreference.com
< cpp‎ | numeric‎ | valarray

template< class T > /*unspecified1*/ begin( valarray<T>& v ); | (1) | (since C++11)
template< class T > /*unspecified2*/ begin( const valarray<T>& v ); | (2) | (since C++11)

The overload of std::begin for `valarray` returns an iterator of unspecified type referring to the first element in the numeric array.

1) The return type meets the requirements of mutable LegacyRandomAccessIterator.
2) The return type meets the requirements of constant LegacyRandomAccessIterator.

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

### Parameters

v | - | a numeric array

### Return value

Iterator to the first value 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: std::begin(v1 + v2) is not portable, std::begin(std::valarray<T>(v1 + v2)) 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

Run this code

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

    auto show = [](std::valarray<int> const& v) {
        std::for_each(std::begin(v), std::end(v), [](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 };

        std::for_each(std::begin(z), std::end(z), [](char c) { 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++!

### See also

std::end(std::valarray) (C++11) | specializes std::end (function template)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/numeric/valarray/begin2&oldid=123438"