Initializing Static Variables in the Constructor

Static class variables cannot be initialized in the constructor of a class because they belong to the class itself, not to any particular instance.

Constructors are used to initialize instance variables, which are unique to each object created from the class.

Static variables, on the other hand, are shared among all instances of the class and are initialized outside of any instance.

Consider this example, which will not compile:

1#include <string>
2#include <iostream>
3
4class Vampire {
5 public:
6  static std::string Faction;  
7
8  Vampire() {
9    // This will not work
10    Faction = "Undead";  
11  }
12};
13
14
15int main() {
16  std::cout << Vampire::Faction;
17}

1error LNK2001: unresolved external symbol Vampire::Faction

Static variables need to be initialized in a context that is not tied to a specific instance of the class:

1#include <string>
2#include <iostream>
3
4class Vampire {
5 public:
6  static std::string Faction;  
7};
8
9// Definition outside the class
10std::string Vampire::Faction{"Undead"};  
11
12int main() {
13  std::cout << Vampire::Faction;
14}

1Undead

Typically, we would initialize static variables at the point of declaration or in a class method. Initialization at the point of declaration looks like this:

1#include <string>
2#include <iostream>
3
4class Vampire {
5 public:
6  static inline std::string Faction{"Undead"};  
7};
8
9int main() {
10  std::cout << Vampire::Faction;
11}

1Undead

In some cases, we may not be able to determine an initial value at the time we’re writing the class. In such scenarios, we can provide a static member function to set its value:

1#include <iostream>
2#include <string>
3
4class Vampire {
5 public:
6  static std::string Faction;
7
8  static void InitializeFaction(std::string F) {
9    Faction = F;
10  }
11};
12
13// Definition outside the class
14std::string Vampire::Faction;

We can then call this function later, once we know what Faction should be set to:

1#include <iostream>
2#include <string>
3
Vampire Class|Show
4class Vampire {/*...*/};
15
16int main() {
17  Vampire::InitializeFaction("Undead");
18  std::cout << Vampire::Faction;
19}

1Undead

In summary, static class variables cannot be initialized in the constructor because they are shared across all instances and belong to the class itself. They should be initialized at the point of declaration or within a class method.