How to iterate std::set?

I have this code:

std::set<unsigned long>::iterator it;
for (it = SERVER_IPS.begin(); it != SERVER_IPS.end(); ++it) {
	u_long f = it; // error here
}

There is no ->first value. How I can obtain the value?

You must dereference the iterator in order to retrieve the member of your set.

std::set<unsigned long>::iterator it;
for (it = SERVER_IPS.begin(); it != SERVER_IPS.end(); ++it) {
    u_long f = *it; // Note the "*" here
}

If you have C++11 features, you can use a range-based for loop:

for(auto f : SERVER_IPS) {
  // use f here
}    

Another example for the C++11 standard:

set<int> data;
data.insert(4);
data.insert(5);

for (const int &number : data)
  cout << number;

Just use the * before it:

set<unsigned long>::iterator it;
for (it = myset.begin(); it != myset.end(); ++it) {
    cout << *it;
}

This dereferences it and allows you to access the element the iterator is currently on.

How do you iterate std::set?

int main(int argc,char *argv[]) 
{
    std::set<int> mset;
    mset.insert(1); 
    mset.insert(2);
    mset.insert(3);

    for ( auto it = mset.begin(); it != mset.end(); it++ )
        std::cout << *it;
}

One more thing that might be useful for beginners is , since std::set is not allocated with contiguous memory chunks , if someone want to iterate till kth element normal way will not work. example:

std::vector<int > vec{1,2,3,4,5};
int k=3;
for(auto itr=vec.begin();itr<vec.begin()+k;itr++) cout<<*itr<<" ";

std::unordered_set<int > s{1,2,3,4,5};
int k=3;
int index=0;
auto itr=s.begin();
while(true){
   if(index==k) break;
   cout<<*itr++<<" ";
   index++;
}