C++ Algorithm fill
The fill function in C++ Algorithm is utilized to set a uniform new value to all elements within a defined range [first, end) through the use of the operator=.
Note: Range [first, last) means first is included in the range but last is not included.
Syntax
template <class ForwardIterator, class T>
void fill (ForwardIterator first, ForwardIterator last, const T& val);
Parameter
A forward iterator indicates the location of the initial element within a defined range.
The last parameter is a forward iterator that points to one position beyond the last element in the specified range that will be iterated over.
The variable "val" represents the value that will be assigned to elements within the range [first, last).
Return value
Complexity
The complexity increases linearly based on the distance between the first and last elements during each assignment.
Data races
The elements within the range [first1, last1) are altered with each element being accessed precisely once.
Exception safety
This function raises an exception if there is an exception during element assignments or operations on an iterator.
Please be aware that using incorrect parameters can result in unpredictable behavior.
Example 1
Let's explore a basic example to showcase the utilization of the fill method:
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v(5);
fill(v.begin(), v.end(), 2);
for_each(v.begin(), v.end(), [](int x) { cout << x << ","; });
return 0;
}
Output:
2,2,2,2,2,
Example 2
Let's see another simple example:
#include <iostream> // std::cout
#include <algorithm> // std::fill
#include <vector> // std::vector
using namespace std;
int main () {
vector<int> myvector (8); // myvector: 0 0 0 0 0 0 0 0
fill (myvector.begin(),myvector.begin()+4,5); // myvector: 5 5 5 5 0 0 0 0
fill (myvector.begin()+3,myvector.end()-2,8); // myvector: 5 5 5 8 8 8 0 0
cout << "myvector contains:";
for (vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
cout << ' ' << *it;
cout << '\n';
return 0;
}
Output:
myvector contains: 5 5 5 8 8 8 0 0
Example 3
Let's see another simple example:
#include <vector>
#include <algorithm>
#include <iostream>
int main( )
{
using namespace std;
vector <int> v1;
vector <int>::iterator Iter1;
int i;
for ( i = 0 ; i <= 9 ; i++ )
{
v1.push_back( 5 * i );
}
cout << "Vector v1 = ( " ;
for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
cout << *Iter1 << " ";
cout << ")" << endl;
// Fill the last 5 positions with a value of 2
fill( v1.begin( ) + 5, v1.end( ), 2 );
cout << "Modified v1 = ( " ;
for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
cout << *Iter1 << " ";
cout << ")" << endl;
return 0;
}
Output:
Vector v1 = ( 0 5 10 15 20 25 30 35 40 45 )
Modified v1 = ( 0 5 10 15 20 2 2 2 2 2 )
Example 4
Let's see another simple example:
#include <algorithm>
#include <vector>
#include <iostream>
#include <iomanip>
using namespace std;
void print(const vector <int>& v)
{
vector <int>::const_iterator i;
for(i = v.begin(); i != v.end(); i++)
{
cout << setw(2) << *i << " ";
}
cout << endl;
}
int main()
{
int arr[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
vector <int> v(arr, arr + sizeof(arr) / sizeof(int));
cout << "Vector before fill" << endl;
print(v);
fill(v.begin() + 4, v.end() - 3, -1);
cout << "Vector after fill" << endl;
print(v);
}
Output:
Vector before fill
0 1 2 3 4 5 6 7 8 9
Vector after fill
0 1 2 3 -1 -1 -1 7 8 9
