Книга: Standard Template Library Programmer

Non-mutating algorithms

for_each

Category: algorithms

Component type: function

template <class InputIterator, class UnaryFunction>
UnaryFunction for_each(InputIterator first, InputIterator last, UnaryFunction f);

For_each applies the function object f to each element in the range [first, last); f's return value, if any, is ignored. Applications are performed in forward order, i.e. from first to last. For_each returns the function object after it has been applied to each element. [1]

Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.

• InputIterator is a model of Input Iterator

• UnaryFunction is a model of Unary Function

• UnaryFunction does not apply any non-constant operation through its argument.

• InputIterator's value type is convertible to UnaryFunction 's argument type.

• [first, last) is a valid range.

Linear. Exactly last – first applications of UnaryFunction.

template<class T> struct print : public unary_function<T, void> {
 print(ostream& out) : os(out), count(0) {}
 void operator() (T x) { os << x << ' '; ++count; }
 ostream& os;
 int count;
};
int main() {
 int A[] = {1, 4, 2, 8, 5, 7};
 const int N = sizeof(A) / sizeof(int);
 print<int> P = for_each(A, A + N, print<int>(cout));
 cout << endl << P.count << " objects printed." << endl;
}

[1] This return value is sometimes useful, since a function object may have local state. It might, for example, count the number of times that it is called, or it might have a status flag to indicate whether or not a call succeeded.

The function object overview, count, copy

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