< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
Defined in header <numeric>
template< class ForwardIt, class T >
void iota( ForwardIt first, ForwardIt last, T value );
(since C++11)
(constexpr since C++20)

Fills the range [firstlast) 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

first, last - 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.

#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 */
    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

a view consisting of a sequence generated by repeatedly incrementing an initial value
(class template) (customization point object)[edit]
copy-assigns the given value to every element in a range
(function template) [edit]
assigns a range of elements a certain value
assigns the results of successive function calls to every element in a range
(function template) [edit]
saves the result of a function in a range
fills a range with successive increments of the starting value