Namespaces
Variants

std:: multiplies<void>

From cppreference.net
C++
Utilities library
Function objects
Function invocation
(C++17) (C++23)
Identity function object
(C++20)
Old binders and adaptors
( until C++17* )
( until C++17* )
( until C++17* )
( until C++17* )
( until C++17* )
( until C++17* )
( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
( until C++20* )
( until C++20* )
( until C++17* ) ( until C++17* )
( until C++17* ) ( until C++17* )

( until C++17* )
( until C++17* ) ( until C++17* ) ( until C++17* ) ( until C++17* )
( until C++20* )
( until C++20* )
定义于头文件 <functional>
template <>
class multiplies < void > ;
(C++14 起)

std:: multiplies < void > 是 std::multiplies 的特化版本，其参数和返回类型由编译器推导得出。

目录

成员类型

类型 定义
is_transparent 未指定

成员函数

operator()
返回两个参数的乘积
(公开成员函数)

std::multiplies<void>:: operator()

template < class T, class U >

constexpr auto operator ( ) ( T && lhs, U && rhs ) const

- > decltype ( std:: forward < T > ( lhs ) * std:: forward < U > ( rhs ) ) ;

返回 lhs 与 rhs 的乘积。

参数

lhs, rhs - 待相乘的值

返回值

std:: forward < T > ( lhs ) * std:: forward < U > ( rhs ) 。

示例

运行此代码 
#include <complex>
#include <functional>
#include <iostream>
int main()
{
    auto complex_multiplies = std::multiplies<void>{}; // “void”可省略
    constexpr std::complex z1{1.0, 2.0}, z2{3.0, 4.0};
    std::cout << std::showpos
              << complex_multiplies(z1, z2) << ' ' << z1 * z2 << '\n'
              << complex_multiplies(z1, 5.) << ' ' << z1 * 5. << '\n'
              << complex_multiplies(5., z1) << ' ' << 5. * z1 << '\n';
}

输出： 

(-5,+10) (-5,+10)
(+5,+10) (+5,+10)
(+5,+10) (+5,+10)