NAME¶

std::begin(std::valarray) - std::begin(std::valarray)

Synopsis¶

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

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 must
* meet the requirements of mutable LegacyRandomAccessIterator,

* model contiguous_iterator, (since C++20)

* have a member type value_type, which is T, and
* have a member type reference, which is T&.
2) The return type must
* meet the requirements of constant LegacyRandomAccessIterator,

* model contiguous_iterator, (since C++20)

* have a member type value_type, which is T, and
* have a member type reference, which is const T&.

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¶

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

void show(const std::valarray<int>& 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};

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
1. begin() was required to support replacement
LWG 2058 C++11 types 1. not required
2. it was unspecified when the returned 2. specified
iterators will be invalidated

See also¶

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