last). [1]
The function object binary_op is not required to be either commutative or associative: the order of all of accumulate's operations is specified. The result is first initialized to init. Then, for each iterator i in [first, last), in order from beginning to end, it is updated by result = result + *i (in the first version) or result = binary_op(result, *i) (in the second version).
Definition Defined in the standard header numeric, and in the nonstandard backward-compatibility header algo.h.
Requirements on types For the first version, the one that takes two arguments:
• InputIterator is a model of Input Iterator.
• T is a model of Assignable.
• If x is an object of type T and y is an object of InputIterator's value type, then x + y is defined.
• The return type of x + y is convertible to T.
For the second version, the one that takes three arguments:
• InputIterator is a model of Input Iterator.
• T is a model of Assignable.
• BinaryFunction is a model of Binary Function.
• T is convertible to BinaryFunction's first argument type.
• The value type of InputIterator is convertible to BinaryFunction's second argument type.
• BinaryFunction's return type is convertible to T.
Preconditions • [first, last) is a valid range.
Complexity Linear. Exactly last – first invocations of the binary operation.
Example int main() {
int A[] = {1, 2, 3, 4, 5};
const int N = sizeof(A) / sizeof(int);
cout << 'The sum of all elements in A is ' << accumulate(A, A + N, 0) << endl;
cout << 'The product of all elements in A is ' << accumulate(A, A + N, 1, multiplies<int>()) << endl;
}
Notes [1] There are several reasons why it is important that accumulate starts with the value init. One of the most basic is that this allows accumulate to have a well-defined result even if [first, last) is an empty range: if it is empty, the return value is init. If you want to find the sum of all of the elements in [first, last), you can just pass 0 as init.
See also inner_product, partial_sum, adjacent_difference, count
Category: algorithms
Component type: function
Prototype Inner_product is an overloaded name; there are actually two inner_product functions.
template <class InputIterator1, class InputIterator2, class T>
T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init);
template <class InputIterator1, class InputIterator2, class T, class BinaryFunction1, class BinaryFunction2>
T inner_product(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, T init, BinaryFunction1 binary_op1, BinaryFunction2 binary_op2);
Description Inner_product calculates a generalized inner product of the ranges [first1, last1) and [first2, last2).
The first version of inner_product returns init plus the inner product of the two ranges [1]. That is, it first initializes the result to init and then, for each iterator i in [first1, last1) , in order from the beginning to the end of the range, updates the result by result = result + (*i) * *(first2 + (i – first1)) .
The second version of inner_product is identical to the first, except that it uses two user-supplied function objects instead of operator+ and operator*. That is, it first initializes the result to init and then, for each iterator i in [first1, last1), in order from the beginning to the end of the range, updates the result by result = binary_op1(result, binary_op2(*i, *(first2 + (i – first1))). [2]
Definition Defined in the standard header numeric, and in the nonstandard backward-compatibility header algo.h.
Requirements on types For the first version:
• InputIterator1 is a model of Input Iterator.
• InputIterator2 is a model of Input Iterator.
• T is a model of Assignable.
• If x is an object of type T, y is an object of InputIterator1's value type, and z is an object of InputIterator2's value type, then x + y * z is defined.
• The type of x + y * z is convertible to T.
For the second version:
• InputIterator1 is a model of Input Iterator.
• InputIterator2 is a model of Input Iterator.
• T is a model of Assignable.
• BinaryFunction1 is a model of Binary Function.
• BinaryFunction2 is a model of Binary Function.
• InputIterator1's value type is convertible to
