Syntax error when initializing a static variable - c++

Question

There are two classes defined..
class Dictionary
{
public:
Dictionary();
Dictionary(int i);
// ...
};
and
class Equation
{
static Dictionary operator_list(1);
// ...
};
but the problem is, whenever I compile this, I get a weird error message
error C2059: syntax error : 'constant'
But it compiles well when I use the default constructor on operator_list.

Answer 1

In C++ you cannot combine declaration and initialization. When you do not specify constructor parameters of operator_list, you do not call its default constructor: you simply declare it. You need to also initialize it in the corresponding C++ file, like this:
Equation.h
class Equation {
static Dictionary operator_list;
};
Equation.cpp:
Dictionary Equation::operator_list(1);
Note the absence of static in the CPP file: it is not there by design. The compiler already knows from the declaration that operator_list is static.
Edit: You have a choice with static constant members of integral and enumerated types: you can initialize them in the CPP file as in the example above, or you can give them a value in the header. You still need to define that member in your C++ file, but you must not give it a value at the definition time.

Answer 2

static Dictionary operator_list(); is a function signature declaring a function returning a Dictionary and taking no arguments, that's why your compiler let you do it.
The reasons static Dictionary operator_list(1); fails is because you can't set a value of an complex type in the declaration of your classes. You need to do this elsewhere (e.g. in the .cpp )
For more information, see this post : https://stackoverflow.com/a/3792427/103916

Answer 3

#include <iostream>
using namespace std;
class Dictionary
{
public:
Dictionary() {}
Dictionary(int i):page(i) {}
void display() { cout << "page is " << page << endl; }
private:
int page;
};
class Equation
{
public:
static Dictionary operator_list;
};
Dictionary Equation::operator_list(1); // static members must be initialized this way...
int main()
{
Equation::operator_list.display();
}
Output is:
page is 1