std::iota
From cppreference.com
| Defined in header <numeric>
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| template< class ForwardIt, class T > void iota( ForwardIt first, ForwardIt last, T value ); |
(since C++11) (constexpr since C++20) |
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Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.
Equivalent operation (assuming ++value returns the incremented value):
*first = value; *++first = ++value; *++first = ++value; *++first = ++value; // repeats until “last” is reached
If any of the following conditions is satisfied, the program is ill-formed:
-
Tis not convertible to the value type ofForwardIt. - The expression ++val is ill-formed, where val is a variable of type
T.
Contents |
[edit] Parameters
| first, last | - | the pair of iterators defining the range of elements to fill with sequentially increasing values starting with value |
| value | - | initial value to store |
[edit] Complexity
Exactly std::distance(first, last) increments and assignments.
[edit] Possible implementation
template<class ForwardIt, class T> constexpr // since C++20 void iota(ForwardIt first, ForwardIt last, T value) { for (; first != last; ++first, ++value) *first = value; } |
[edit] Notes
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.
[edit] Example
The following example applies std::shuffle to a vector of std::lists' iterators. std::iota is used to populate containers.
Run this code
#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 (const auto& n : l) std::cout << std::setw(2) << n << ' '; std::cout << '\n'; std::cout << "Contents of l, viewed via shuffled v:\t"; for (const auto 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
[edit] See also
| (C++23) |
fills a range with successive increments of the starting value (algorithm function object) |
| copy-assigns the given value to every element in a range (function template) | |
| (C++20) |
assigns a range of elements a certain value (algorithm function object) |
| 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 (algorithm function object) |
| (C++20) |
a view consisting of a sequence generated by repeatedly incrementing an initial value(class template) (customization point object) |
a view that maps each element of adapted sequence to a tuple of both the element's position and its value(class template) (range adaptor object) |
