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std::generate() algorithm

// (1)
template< class ForwardIt, class Generator >
constexpr void generate( ForwardIt first, ForwardIt last, Generator g );

// (2)
template< class ExecutionPolicy, class ForwardIt, class Generator >
void generate( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last, Generator g );
  • (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.

Overload Resolution

These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od C++20) is true.

Parameters

first
last

The range of elements to generate.

policy

The execution policy to use. See execution policy for details.

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

ForwardItLegacyForwardIterator

Return value

(none)

Complexity

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

Exceptions

The overloads with a template parameter named ExecutionPolicy report 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 none other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

generate (1)
template<class ForwardIt, class Generator>
constexpr //< since C++20
void generate(ForwardIt first, ForwardIt last, Generator g)
{
for (; first != last; ++first)
*first = g();
}

Examples

Main.cpp
#include <algorithm>
#include <iostream>
#include <vector>

void println(std::string_view fmt, auto const& v)
{
for (std::cout << fmt; auto const& 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
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Hover to see the original license.

std::generate() algorithm

// (1)
template< class ForwardIt, class Generator >
constexpr void generate( ForwardIt first, ForwardIt last, Generator g );

// (2)
template< class ExecutionPolicy, class ForwardIt, class Generator >
void generate( ExecutionPolicy&& policy,
ForwardIt first, ForwardIt last, Generator g );
  • (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.

Overload Resolution

These overloads participate in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>  (do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>  (od C++20) is true.

Parameters

first
last

The range of elements to generate.

policy

The execution policy to use. See execution policy for details.

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

ForwardItLegacyForwardIterator

Return value

(none)

Complexity

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

Exceptions

The overloads with a template parameter named ExecutionPolicy report 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 none other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

generate (1)
template<class ForwardIt, class Generator>
constexpr //< since C++20
void generate(ForwardIt first, ForwardIt last, Generator g)
{
for (; first != last; ++first)
*first = g();
}

Examples

Main.cpp
#include <algorithm>
#include <iostream>
#include <vector>

void println(std::string_view fmt, auto const& v)
{
for (std::cout << fmt; auto const& 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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.