for_each loop in C++
Last Updated :
12 Jul, 2021
Apart from the generic looping techniques, such as “for, while and do-while”, C++ in its language also allows us to use another functionality which solves the same purpose termed “for-each” loops. This loop accepts a function which executes over each of the container elements. This loop is defined in the header file “algorithm”: #include<algorithm>, and hence has to be included for successful operation of this loop.
- It is versatile, i.e. Can work with any container.
- It reduces chances of errors one can commit using generic for loop
- It makes code more readable
- for_each loops improve overall performance of code
-
Syntax:
for_each (InputIterator start_iter, InputIterator last_iter, Function fnc)
start_iter : The beginning position
from where function operations has to be executed.
last_iter : The ending position
till where function has to be executed.
fnc/obj_fnc : The 3rd argument is a function or
an object function which operation would be applied to each element.
CPP
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
void printx2( int a)
{
cout << a * 2 << " " ;
}
struct Class2
{
void operator() ( int a)
{
cout << a * 3 << " " ;
}
} ob1;
int main()
{
int arr[5] = { 1, 5, 2, 4, 3 };
cout << "Using Arrays:" << endl;
cout << "Multiple of 2 of elements are : " ;
for_each(arr, arr + 5, printx2);
cout << endl;
cout << "Multiple of 3 of elements are : " ;
for_each(arr, arr + 5, ob1);
cout << endl;
vector< int > arr1 = { 4, 5, 8, 3, 1 };
cout << "Using Vectors:" << endl;
cout << "Multiple of 2 of elements are : " ;
for_each(arr1.begin(), arr1.end(), printx2);
cout << endl;
cout << "Multiple of 3 of elements are : " ;
for_each(arr1.begin(), arr1.end(), ob1);
cout << endl;
}
|
Output
Using Arrays:
Multiple of 2 of elements are : 2 10 4 8 6
Multiple of 3 of elements are : 3 15 6 12 9
Using Vectors:
Multiple of 2 of elements are : 8 10 16 6 2
Multiple of 3 of elements are : 12 15 24 9 3
Exceptions and for_each:
In the cases of exceptions, if the function throws an exception or if any of the operations on iterators throws an exception, for_each loop will also throw an exception and break/terminate the loop.
Note:
- Invalid arguments may leads to Undefined behavior.
- For_each can not work with pointers of an array (An array pointer do not know its size, for_each loops will not work with arrays without knowing the size of an array)
CPP
#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
void printx2( int a)
{
cout << a * 2 << " " ;
if ( a % 2 == 0)
{
throw a;
}
}
struct Class2
{
void operator() ( int a)
{
cout << a * 3 << " " ;
if ( a % 2 == 0)
{
throw a;
}
}
} ob1;
int main()
{
int arr[5] = { 1, 5, 2, 4, 3 };
cout << "Using Array" << endl;
try
{
for_each(arr, arr + 5, printx2);
}
catch ( int i)
{
cout << "\nThe Exception element is : " << i ;
}
cout << endl;
try
{
for_each(arr, arr + 5, ob1);
}
catch ( int i)
{
cout << "\nThe Exception element is : " << i ;
}
vector< int > arr1 = { 1, 3, 6, 5, 1 };
cout << "\nUsing Vector" << endl;
try
{
for_each(arr1.begin(), arr1.end(), printx2);
}
catch ( int i)
{
cout << "\nThe Exception element is : " << i ;
}
cout << endl;
try
{
for_each(arr1.begin(), arr1.end(), ob1);
}
catch ( int i)
{
cout << "\nThe Exception element is : " << i ;
}
}
|
Output
Using Array
2 10 4
The Exception element is : 2
3 15 6
The Exception element is : 2
Using Vector
2 6 12
The Exception element is : 6
3 9 18
The Exception element is : 6
Using Lambdas:
With the introduction of lambda functions, this can be easily used to make the whole thing inline which is very compact and useful for people looking for using functional programming.
C++
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
int main()
{
vector< int > vec{ 1, 2, 3, 4, 5 };
for_each(vec.begin(), vec.end(), []( int & a) { a++; });
for_each(vec.begin(), vec.end(),
[]( int a) { cout << a << " " << endl; });
return 0;
}
|
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