for_each
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Category: algorithms |
Component type: function |
Prototype
template <class InputIterator, class UnaryFunction>
UnaryFunction for_each(InputIterator first, InputIterator last, UnaryFunction f);
Description
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]
Definition
Defined in the standard header algorithm, and in the nonstandard
backward-compatibility header algo.h.
Requirements on types
-
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.
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InputIterator's value type is convertible to UnaryFunction's
argument type.
Preconditions
-
[first, last) is a valid range.
Complexity
Linear. Exactly last - first applications of UnaryFunction.
Example
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;
}
Notes
[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.
See also
The function object overview, count, copy
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1999 Silicon Graphics, Inc. All Rights Reserved.
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