std::iota

 

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copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) fill fill_n transform generate generate_n removeremove_if remove_copyremove_copy_if	replacereplace_if replace_copyreplace_copy_if swap swap_ranges iter_swap reverse reverse_copy rotate rotate_copy random_shuffleshuffle  (C++11) unique unique_copy
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iota (C++11) accumulate inner_product	adjacent_difference partial_sum
C library
qsort	bsearch

 

Defined in header <numeric>
template< class ForwardIterator, class T > void iota( ForwardIterator first, ForwardIterator last, T value );		(since C++11)

Fills the range [first, last) with sequentially increasing values, starting with value and repetitively evaluating ++value.

Equivalent operation:

*(d_first)   = value;
*(d_first+1) = ++value;
*(d_first+2) = ++value;
*(d_first+3) = ++value;
...

Parameters

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

Return value

(none)

Complexity

Exactly last - first increments and assignments.

Possible implementation

template<class ForwardIterator, class T> void iota(ForwardIterator first, ForwardIterator last, T value) { while(first != last) { *first++ = value; ++value; } }

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 eventually made it into the standard library in C++11.

Example

The following example applies std::random_shuffle to a vector of iterators to a std::list since std::random_shuffle cannot be applied to an std::list directly. std::iota is used to create the vector.

Run this code

#include <numeric>
#include <algorithm>
#include <list>
#include <vector>
#include <iostream>
 
int main()
{
    std::list<int> l(10);
    std::iota(l.begin(), l.end(), -4);
 
    std::vector<std::list<int>::iterator> v(l.size());
    std::iota(v.begin(), v.end(), l.begin());
 
    std::random_shuffle(v.begin(), v.end());
 
    std::cout << "Contents of the list: ";
    for(auto n: l) {
        std::cout << n << ' ';
    }
    std::cout << '\n';
 
    std::cout << "Contents of the list, shuffled: ";
    for(auto i: v) {
        std::cout << *i << ' ';
    }
    std::cout << '\n';
}

Output:

Contents of the list: -4 -3 -2 -1 0 1 2 3 4 5
Contents of the list, shuffled: 0 -1 3 4 -4 1 -2 -3 2 5

See also

fill	assigns a range of elements a certain value (function template)
generate	saves the result of a function in a range (function template)