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    std::generate

    From cppreference.com
     
    C++
     
    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
    (C++17)
    Search operations
    (C++11)                (C++11)(C++11)

    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    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
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations
    C library
    Numeric operations
    Operations on uninitialized memory
     
    Defined in header <algorithm>
    template< class ForwardIt, class Generator > void generate( ForwardIt first, ForwardIt last, Generator g );
    		 (1) (constexpr since C++20)
    template< class ExecutionPolicy, class ForwardIt, class Generator > void generate( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Generator g );
    		 (2) (since C++17)
    1) Assigns each element in range [first, last) a value generated by the given function object g.
    2) Same as (1), but executed according to policy.
    This overload participates in overload resolution only if all following conditions are satisfied:

    std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

    		(until C++20)

    std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.

    		(since C++20)

    Parameters

    first, last - the pair of iterators defining the range of elements to generate
    policy - the execution policy to use
    g - generator function object that will be called.

    The signature of the function should be equivalent to the following:

    Ret fun();

    The type Ret must be such that an object of type ForwardIt can be dereferenced and assigned a value of type Ret. ​

    Type requirements
    -
    ForwardIt must meet the requirements of LegacyForwardIterator.

    Complexity

    Exactly std::distance(first, last) invocations of g() and assignments.

    Exceptions

    The overload with a template parameter named ExecutionPolicy reports errors as follows:

    • If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
    • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

    Possible implementation

    template<class ForwardIt, class Generator>
constexpr //< since C++20
void generate(ForwardIt first, ForwardIt last, Generator g)
{
    for (; first != last; ++first)
        *first = g();
}

    Example

    Run this code
    #include <algorithm>
#include <iostream>
#include <vector>

void println(std::string_view fmt, const auto& v)
{
    for (std::cout << fmt; const auto& e : v)
        std::cout << e << ' ';
    std::cout << '\n';
};


int f()
{
    static int i;
    return ++i;
}

int main()
{
    std::vector<int> v(5);
    
    std::generate(v.begin(), v.end(), f);
    println("v: ", v);
    
    // Initialize with default values 0,1,2,3,4 from a lambda function
    // Equivalent to std::iota(v.begin(), v.end(), 0);
    std::generate(v.begin(), v.end(), [n = 0] () mutable { return n++; });
    println("v: ", v);
}

    Output: 

    v: 1 2 3 4 5
v: 0 1 2 3 4

    See also

    		 copy-assigns the given value to every element in a range
    (function template) [edit]
    		assigns the results of successive function calls to N elements in a range
    (function template) [edit]
    (C++11)
    		 fills a range with successive increments of the starting value
    (function template) [edit]
    (C++20)
    		 saves the result of a function in a range
    (algorithm function object)[edit]