Defined in header <numeric> | ||
|---|---|---|
template< class ForwardIt, class T > void iota( ForwardIt first, ForwardIt last, T value ); | (since C++11) (until C++20) | |
template< class ForwardIt, class T > constexpr void iota( ForwardIt first, ForwardIt last, T value ); | (since C++20) |
Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.
Equivalent operation:
*(first) = value; *(first + 1) = ++value; *(first + 2) = ++value; *(first + 3) = ++value; ...
| first, last | - | the range of elements to fill with sequentially increasing values starting with value |
| value | - | initial value to store; the expression ++value must be well-formed |
(none).
Exactly last - first increments and assignments.
template<class ForwardIt, class T>
constexpr // since C++20
void iota(ForwardIt first, ForwardIt last, T value)
{
while (first != last)
{
*first++ = value;
++value;
}
} |
The function is named after the integer function ⍳ from the programming language APL. It was one of the STL components that were not included in C++98, but made it into the standard library in C++11.
The following example applies std::shuffle to a vector of std::lists' iterators. std::iota is used to populate containers.
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <list>
#include <numeric>
#include <random>
#include <vector>
class BigData // inefficient to copy
{
int data[1024]; /* some raw data */
public:
explicit BigData(int i = 0) { data[0] = i; /* ... */ }
operator int() const { return data[0]; }
BigData& operator=(int i) { data[0] = i; return *this; }
/* ... */
};
int main()
{
std::list<BigData> l(10);
std::iota(l.begin(), l.end(), -4);
std::vector<std::list<BigData>::iterator> v(l.size());
std::iota(v.begin(), v.end(), l.begin());
// Vector of iterators (to original data) is used to avoid expensive copying,
// and because std::shuffle (below) cannot be applied to a std::list directly.
std::shuffle(v.begin(), v.end(), std::mt19937 {std::random_device{}()});
std::cout << "Original contents of the list l:\t";
for (auto const& n : l) std::cout << std::setw(2) << n << ' ';
std::cout << '\n';
std::cout << "Contents of l, viewed via shuffled v:\t";
for (auto const i : v) std::cout << std::setw(2) << *i << ' ';
std::cout << '\n';
}Possible output:
Original contents of the list l: -4 -3 -2 -1 0 1 2 3 4 5 Contents of l, viewed via shuffled v: -1 5 -4 0 2 1 4 -2 3 -3
|
(C++20) | a view consisting of a sequence generated by repeatedly incrementing an initial value (class template) (customization point object) |
| copy-assigns the given value to every element in a range (function template) |
|
|
(C++20) | assigns a range of elements a certain value (niebloid) |
| assigns the results of successive function calls to every element in a range (function template) |
|
|
(C++20) | saves the result of a function in a range (niebloid) |
|
(C++23) | fills a range with successive increments of the starting value (niebloid) |
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