From cppreference.com
iteratorbegin(); (1) (since C++11)const_iteratorbegin()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
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
to work with valarrays, not to provide container semantics.
Example
Run this code
#include<algorithm>#include<iostream>#include<valarray>voidshow(conststd::valarray<int>&v){std::for_each(v.begin(),v.end(),[](intc){std::cout<<c<<' ';});std::cout<<'\n';};intmain(){conststd::valarray<int>x{47,70,37,52,90,23,17,33,22,16,21,4};conststd::valarray<int>y{25,31,71,56,21,21,15,34,21,27,12,6};show(x);show(y);conststd::valarray<int>z{x+y};for(charc: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
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
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)
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