Populate a static member container in c++

Question

I've got a static class member which is some container, like

(Foo.h)

class Foo
{
   ...
private:
   static list<string> s_List;
}

I need to populate the list with a number of specific values. Actually it should be also const, but that might overcomplicate the problem further. All the class member functions are static, so initializing it in a constructor doesn't make sense.

Answer 1

The ways I(the author of the question) have vainly tried to do this.

---

I tried to do smth like (in Foo.cpp):

list<string> Foo::s_List = list<string>();
Foo::s_List.insert("apple");
Foo::s_List.insert("bannana");
Foo::s_List.insert("grapes");

But that gives a compiler error.

---

Then I thought of making an Initialize() method and calling it right from the code

void Foo::Initialize()
{
    s_List.insert("rats");
    s_List.insert("cats");
}

Foo::Initialize();

// error: compiler considers it to be a redefenition of the method, not a call.

---

The only viable idea left (havent yet tried) would be to check if the list is empty in each method that uses it, and if it's the case, call Initialize(). But that's ugly!

Answer 2

one possible solution would be to use an accessor method that checks to see if it is initialized, and does so if it isn't.

Answer 3

Another alternative is to create a simple initialiser class:

list <string> Foo::s_List;

struct Init {
   Init() {
      Foo::s_List.insert("apple");
      Foo::s_List.insert("bannana");
      Foo::s_List.insert("grapes");
   }
};

static Init doInit;

Note that, as the list is private, this will probably require you to make Init a friend of Foo. It's also often convenient to make such classes be contained by the class they are initialising.

However, I just re-read your question and another thought occurs - if the list is const, you will presumably not be changing it, in which case a simple array of strings, initialised with the strings in sorted order may be a better solution. It will certainly be faster to search (using std::binary_search) than a list, and can of course be easily initialised.

Answer 4

a common solution is to do something like this:

// header
class Foo
{
...
private:
   static list<string> s_List;
}

// cpp
list<string> init()
{
     list<string> tmp;
     ... fill tmp with strings

     return tmp;
 }

 list<string> Foo::s_List(init());

the other method is like Neil Butterworth suggested.

Answer 5

It depends on what values you need to put in that list. Are they static or do they require some form of computation?

If they are static, you can do this:

namespace {
   const char* const initVals[] = { "A", "B", "C" };
}

list<string> Foo::s_list(initVals, initVals + 3);