C++ set begin
C++ set begin function is used to return an iterator referring to the first element of the set container.
Syntax
iterator begin(); //until C++ 11
const_iterator begin() const; //until C++ 11
iterator begin() noexcept; //since C++ 11
const_iterator begin() const noexcept; //since C++ 11
Parameter
Return value
It returns an iterator pointing to the first element of the set.
Complexity
Constant.
Iterator validity
No changes.
Data Races
The container is accessed. Neither the constant nor the non-constant versions modify the container.
Exception Safety
This function never throws exceptions.
Example 1
Let's see the simple example for begin function:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
set<string> myset= {"Java", "C++", "SQL"};
// show content:
cout<<"Contents of myset are: "<<endl;
for (set<string>::iterator it=myset.begin(); it!=myset.end(); ++it)
cout << *it<< '\n';
return 0;
}
Output:
Contents of myset are:
C++
Java
SQL
In the above example, begin function is used to return an iterator pointing to the first element in the myset set.
Example 2
Let's see a simple example:
#include <iostream>
#include <set>
using namespace std;
int main()
{
set<int> c;
c.insert(5);
c.insert(2);
c.insert(4);
c.insert(1);
c.insert(0);
c.insert(9);
set<int>::iterator i = c.begin();
while (i != c.end())
cout << *i++ << " ";
cout << endl;
}
Output:
0 1 2 4 5 9
Example 3
Let's see a simple example to iterate over the set using while loop:
#include <iostream>
#include <set>
#include <string>
int main()
{
using namespace std;
set<string> myset = { "Nikita","Deep","Priya","Suman","Aman" };
cout<<"Elements of myset are: "<<endl;
set<string>::const_iterator it; // declare an iterator
it = myset.begin(); // assign it to the start of the set
while (it != myset.end()) // while it hasn't reach the end
{
cout << *it << "\n";
// print the value of the element icpp tutorials to
++it; // and iterate to the next element
}
cout << endl;
}
Output:
Elements of myset are:
Aman
Deep
Nikita
Priya
Suman
In the above, begin function is used to return an iterator pointing to the first element in the myset set.
Example 4
Let's see a simple example:
#include <set>
#include <iostream>
int main( )
{
using namespace std;
set <int> s1;
set <int>::iterator s1_Iter;
s1.insert( 1 );
s1.insert( 2 );
s1.insert( 3 );
s1_Iter = s1.begin( );
cout << "The first element of s1 is " << *s1_Iter << endl;
s1_Iter = s1.begin( );
s1.erase( s1_Iter );
s1_Iter = s1.begin( );
cout << "The first element of s1 is now " << *s1_Iter << endl;
}
Output:
The first element of s1 is 1
The first element of s1 is now 2
In the above example, begin function is used to return an iterator pointing to the first element in the myset set.