for_each

Performs an operation for each element

Definition

The for_each() algorithm is defined in the standard header <algorithm>, and in the nonstandard backward-compatibility header <algo.h>.

Interface

#include <algorithm>
template < class InputIterator, class Function>
   Function for_each (
    InputIterator first,
    InputIterator last,
    Function f
    );

Parameters:

Parameter	Description
first	An input iterator addressing the position of the first element in the range to be operated on
last	An input iterator addressing the position one past the final element in the range operated on
f	User-defined function object that is applied to each element in the range

Description

The for_each() algorithm applies a specified function object to each element in a forward order within a range.

Return Value

Returns the function object.

Complexity

The complexity is linear, performing exactly (last - first) applications of f.

References

http://www.tenouk.com

Example 1

Problem

The following example uses a lambda function to increment all of the elements of a vector and then computes a sum of them.

Workings

#include <vector>
#include <algorithm>

struct Sum {
    Sum() { sum = 0; }
    void operator()(int n) { sum += n; }
 
    int sum;
};

int main()
{
    std::vector<int> nums{3, 4, 2, 9, 15, 267};
 
    std::cout << "before: ";
    for (auto n : nums) {
        std::cout << n << " ";
    }
    std::cout << '\n';
 
    std::for_each(nums.begin(), nums.end(), [](int &n){ n++; });
    Sum s = std::for_each(nums.begin(), nums.end(), Sum());
 
    std::cout << "after:  ";
    for (auto n : nums) {
        std::cout << n << " ";
    }
    std::cout << '\n';
    std::cout << "sum: " << s.sum << '\n';
   
    return 0;
}

Solution

Output:

before: 3 4 2 9 15 267
after: 4 5 3 10 16 268
sum: 306

References

http://en.cppreference.com

Example 2

Problem

This program illustrates the use of the STL for_each() algorithm to find the cube of each value in a vector of integers. We also use the for_each() algorithm to display the values in the vector.

Workings

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
  vector<int> v(a, a+10);
  
  cout << "\nHere are the initial contents of v:\n";
  for_each(v.begin(), v.end(), DoDisplay);

  cout << "\nAnd here are the cubes of the values in v:\n";
  for_each(v.begin(), v.end(), DoCube);
  for_each(v.begin(), v.end(), DoDisplay);

  return 0;
}

Solution

Output:

Here are the initial contents of v:
1 2 3 4 5 6 7 8 9 10

And here are the cubes of the values in v:
1 8 27 64 125 216 343 512 729 1000

References

http://www.smu.ca/academic/science/compsci

Definition

Interface

Description

Return Value

Complexity

References

Example 1

Example 2

See Also