std::valarray<T>::begin
iterator begin();
|
(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
| v | - | a numeric array |
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 types2. 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
|
See also
(C++11) |
obtains the past-the-end iterator of valarray (public member function) |