C++ std::set and std::multiset Inserting values in a set
Example
Three different methods of insertion can used with sets.
- First, a simple insert of the value. This method returns a pair allowing the caller to check whether the insert really occurred.
- Second, an insert by giving a hint of where the value will be inserted. The objective is to optimize the insertion time in such a case, but knowing where a value should be inserted is not the common case. Be careful in that case; the way to give a hint differs with compiler versions.
- Finally you can insert a range of values by giving a starting and an ending pointer. The starting one will be included in the insertion, the ending one is excluded.
#include <iostream>
#include <set>
int main ()
{
std::set<int> sut;
std::set<int>::iterator it;
std::pair<std::set<int>::iterator,bool> ret;
// Basic insert
sut.insert(7);
sut.insert(5);
sut.insert(12);
ret = sut.insert(23);
if (ret.second==true)
std::cout << "# 23 has been inserted!" << std::endl;
ret = sut.insert(23); // since it's a set and 23 is already present in it, this insert should fail
if (ret.second==false)
std::cout << "# 23 already present in set!" << std::endl;
// Insert with hint for optimization
it = sut.end();
// This case is optimized for C++11 and above
// For earlier version, point to the element preceding your insertion
sut.insert(it, 30);
// inserting a range of values
std::set<int> sut2;
sut2.insert(20);
sut2.insert(30);
sut2.insert(45);
std::set<int>::iterator itStart = sut2.begin();
std::set<int>::iterator itEnd = sut2.end();
sut.insert (itStart, itEnd); // second iterator is excluded from insertion
std::cout << std::endl << "Set under test contains:" << std::endl;
for (it = sut.begin(); it != sut.end(); ++it)
{
std::cout << *it << std::endl;
}
return 0;
}
Output will be:
# 23 has been inserted!
# 23 already present in set!
Set under test contains:
5
7
12
20
23
30
45
