std::iota - cppreference.com (original) (raw)

| | | | | -------------------------------------------------------------------------------------------- | | ------------------------------------- | | template< class ForwardIt, class T > void iota( ForwardIt first, ForwardIt last, T value ); | | (since C++11) (constexpr since C++20) |

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:

• T is not convertible to the value type of ForwardIt.
• The expression ++val is ill-formed, where val is a variable of type T.

[edit] Parameters

[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.

#include #include #include #include #include #include #include   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 l(10); std::iota(l.begin(), l.end(), -4);   std::vector<std::list::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