for_each()

Library:  Algorithms

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Algorithm that applies a function to each element in a range

#include <algorithm>

namespace std {
  template <class InputIterator, class Function>
  void Function for_each(InputIterator start, 
                         InputIterator finish,
                         Function f);
}

The for_each() algorithm applies the function object f to each value in the range [start, finish), where start and finish are iterators that define the sequence. Since this a non-mutating algorithm, the function f cannot make any modifications to the sequence, but it can achieve results through side effects (such as copying or printing). If f returns a result, the result is ignored.

for_each() returns the function object f.

The function object f is applied exactly finish - start times.

//
// for_each.cpp
//

#include <algorithm>    // for for_each
#include <functional>   // for less, unary_function
#include <iostream>     // for cout, endl
#include <set>          // for set



// Function object that outputs its argument times x.
template <class Arg>
class out_times_x:  public std::unary_function<Arg, void>
{
    Arg multiplier;
public:
    out_times_x(const Arg &x) : multiplier (x) { }

    void operator()(const Arg &x) const {
        std::cout << x * multiplier << " " << std::endl;
    }
};


int main ()
{
    // Typedef for convenience.
    typedef std::set<int, std::less<int>, 
                     std::allocator<int> > sequence;
    
    sequence::value_type arr [] = { 1, 2, 3, 4, 5 };

    // Populate a sequence from arr.
    sequence s(arr, arr + sizeof arr / sizeof *arr);

    // Construct a function object.
    out_times_x<sequence::value_type> f2(2);
  
    // Apply function object's operator() to each element.
    std::for_each(s.begin(), s.end(), f2);
  
    return 0;
}


Program Output

2 
4 
6 
8 
10 

Algorithms, Function Objects

ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.1.1