std::inner_product
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<tbody> </tbody> template< class InputIt1, class InputIt2, class T > T inner_product( InputIt1 first1, InputIt1 last1, InputIt2 first2, T value ); |
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template< class InputIt1, class InputIt2, class T, class BinaryOperation1, class BinaryOperation2 > T inner_product( InputIt1 first1, InputIt1 last1, InputIt2 first2, T value, BinaryOperation1 op1, BinaryOperation2 op2 ); |
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(.. )
[first1, last1) first2. operator* operator+ , op2 op1 .:
Computes inner product (i.e. sum of products) of the range
[first1, last1) and another range beginning at first2. The first version uses operator* to compute product of the element pairs and operator+ to sum up the products, the second version uses op2 and op1 for these tasks respectively.| first1, last1 | ||
| first2 | ||
| value | ||
| op1 | binary operation function object that will be applied. , op2 . : This function takes a value returned by op2 and the current value of the accumulator and produces a new value to be stored in the accumulator. The signature of the function should be equivalent to the following:
The signature does not need to have | |
| op2 | binary operation function object that will be applied. . The signature of the function should be equivalent to the following:
The signature does not need to have | |
-InputIt1, InputIt2 InputIterator.
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-T CopyAssignable CopyConstructible.
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.
template<class InputIt1, class InputIt2, class T>
T inner_product(InputIt1 first1, InputIt1 last1,
InputIt2 first2, T value)
{
while (first1 != last1) {
value = value + *first1 * *first2;
++first1;
++first2;
}
return value;
}
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template<class InputIt1, class InputIt2,
class T,
class BinaryOperation1, class BinaryOperation2>
T inner_product(InputIt1 first1, InputIt1 last1,
InputIt2 first2, T value,
BinaryOperation1 op1
BinaryOperation2 op2)
{
while (first1 != last1) {
value = op1(value, op2(*first1, *first2));
++first1;
++first2;
}
return value;
}
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#include <numeric>
#include <iostream>
#include <vector>
#include <functional>
int main()
{
std::vector<int> a{0, 1, 2, 3, 4};
std::vector<int> b{5, 4, 2, 3, 1};
int r1 = std::inner_product(a.begin(), a.end(), b.begin(), 0);
std::cout << "Inner product of a and b: " << r1 << '\n';
int r2 = std::inner_product(a.begin(), a.end(), b.begin(), 0,
std::plus<int>(), std::equal_to<int>());
std::cout << "Number of pairwise matches between a and b: " << r2 << '\n';
}
:
Inner product of a and b: 21
Number of pairwise matches between a and b: 2
.
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