std::generate
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C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Algorithm library
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
(C++17)
(C++17) (C++17)(C++17)(C++20)
(C++17)
(C++11)
generate
(until C++17)(C++11)
(C++20)(C++20)
(C++17)
(C++17)
(C++17)
(C++17)
Defined in header
<algorithm>
template< class ForwardIt, class Generator >
void generate( ForwardIt first, ForwardIt last, Generator g );
(1)
(constexpr since C++20)
void generate( ForwardIt first, ForwardIt last, Generator g );
template< class ExecutionPolicy, class ForwardIt, class Generator >
(2)
(since C++17)
void generate( ExecutionPolicy&& policy,
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)[edit] 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.
[edit] Complexity
Exactly std::distance (first, last) invocations of g() and assignments.
[edit] 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
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] 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(); }
[edit] 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
[edit] See also
assigns the results of successive function calls to N elements in a range
(function template) [edit]
(function template) [edit]