using std::list with a structure

[TheLionKing]

if i have a struct like this

struct combi_t
{
 int val0;
 int val1;
 int val2;
 combi_t* nextPtr;

and i want to implement std::list loading types of combi_t,
so i do

std::list<combi_t> head;

how do i load each member of combi t into head ? at every head.push_back() how do i add members val0, val1, val2? thanks in advance

[2kaud]

One way is to implement a constructor for combi_t. Example

#include <list>
using namespace std;

struct combi_t
{
	int val0;
	int val1;
	int val2;
	combi_t* nextPtr;

	combi_t(int v0 = 0, int v1 = 0, int v2 = 0, combi_t* np = nullptr) : val0(v0), val1(v1), val2(v2), nextPtr(np) {}
};

int main()
{
list<combi_t> head;

	head.push_back(combi_t(1, 2, 3));
	head.push_back(combi_t(2, 3, 4));
}

[TheLionKing]

I knew you Master 2kaud will save the day! you who gives the correct answer all the time and you save my a** from hotwaters!
THANK YOU AGAIN!

[TheLionKing]

excuse me Master 2kaud,
what about accessing individual values of a type combi_t?
let say i have a function
void do_something(int) ;

and i want to call do_something 3 times but with each member of a type combi_t...
how do i do that? thanks in advance

if i had implemented my own list i could have done something like ptr->val0, ptr->val1, etc

[2kaud]

One simple way is as below. If you are after something different you'll need to provide more details.

combi_t ct(3, 4, 5);

	do_something(ct.val0);
	do_something(ct.val1);
	do_something(ct.val2);

[TheLionKing]

thanks again sir!!!

[TheLionKing]

excuse me again master a lil problem just popped up
implemented the struct like you taught..
i have a

std::list<combi_t > head;
std::vector<int> ups={2,3,4,5,6,7,8 ,9,};
void make_three_sures (std::vector <int> & cross)
{
 for(auto p = cross.begin() ; p != cross.end(); p++)
    {
     for(auto pt = cross.begin()++; pt != cross.end() ; pt++)
        {
         head.push_back(combi_t( *p, *pt, *(pt++) ) );
        }
    }

}

int main()
{
  make_three_sures(ups);
      for (auto ptr = head.begin(); ptr != head.end() ; ptr = ptr++)
          {
           master_roller(combi_t.v0, combi_t.v1, combi_t.v2, num); //this call is wrong!!!
          }
}

how can i go about it in this particula situation? sorry for the disturbances and thanks in advance

[2kaud]

master_roller(combi_t.v0, combi_t.v1, combi_t.v2, num); //this call is wrong!!!

combi_t is a class type, not a variable of a class instance. In my simple example in post #5, ct is the class instance. I suspect you need

master_roller(ptr->val0, ptr->val1, ptr->val2, num);

as ptr is a pointer to an instance of class type combi_t (rather than being an actual instance).

You could also have (not tried)

for (const auto& val : head) 
     master_roller(val.val0, val.val1, val.val2);

[TheLionKing]

ok thanks..
i was doing try and error and did this

for (auto ptr = head.begin(); ptr != head.end() ; ptr = ptr++)
{ combi_t ct = *ptr;
master_roller(ct.val1, ct.val1, ct.val2, num);
}

seems to work, now let me look into yours too..thanks soooo much!!!

[TheLionKing]

None of those solutions worked master, compiler telling me v0 not a member type, or val0 not a member type,
what worked was

for (auto ptr = head.begin(); ptr != head.end() ; ptr = ptr++)
{ combi_t ct = *ptr;
master_roller(ct.val1, ct.val1, ct.val2, num);
}

thank you a lot master 2kaud, the best ever on this site!!!

[2kaud]

None of those solutions worked master, compiler telling me v0 not a member type, or val0 not a member type,
what worked was


thank you a lot master 2kaud, the best ever on this site!!!

Yes, I realised after I posted as I was just using v0, v1 etc from your post #7. As you say, it should be val0, val1 etc as per my changed code in post #8.

[TheLionKing]

ok sir! you're the best, in terms of knowledge and most important,PATIENCE!!!
thanks so much and keep up the good work!

[2kaud]

For completeness. Example of two ways of iterating a container (c++11)

#include <list>
#include <iostream>
#include <iomanip>
using namespace std;

struct combi_t
{
	int val0;
	int val1;
	int val2;
	combi_t* nextPtr;

	combi_t(int v0, int v1, int v2, combi_t* np = nullptr) : val0(v0), val1(v1), val2(v2), nextPtr(np) {}
};

void master_roller(int v0, int v1, int v2)
{
	cout << setw(7) << v0 << setw(7) << v1 << setw(7) << v2 << endl;
}

int main()
{
list<combi_t> head;

	head.push_back(combi_t(1, 2, 3));
	head.push_back(combi_t(2, 3, 4));

	for (const auto& v : head)
		master_roller(v.val0, v.val1, v.val2);

	for (auto pt = head.cbegin(); pt != head.cend(); ++pt)
		master_roller(pt->val0, pt->val1, pt->val2);
}

[TheLionKing]

thank you sir!
since we're already at it, another last question, so i implemented this two versions of codes to make a three combinations of numbers...
i really think they don't work well and now is it looping like mad..can you modify it a lil bit to make it better?

void make_three_sures (std::vector<int> & cross)
{
 /*for(auto p = cross.begin() ; p != cross.end(); p++)
    {
     for(auto pt = cross.begin()++; pt != cross.end() ; pt++)
        {
         head.push_back(combi_t( *p, *pt, *(pt++) ) );
        }
    }*/

for (int p = 0; p < cross.size(); p++)
   {  for(int pt = (p+1); pt < cross.size(); pt++)

      { if (pt>cross.size()) break;;
      head.push_back(combi_t( cross[p], cross[pt], cross[pt++]) );
      }
   }


}

[2kaud]

What are you trying to achieve?