Question

For the following code:

class A
{
public:
static const int VAL;
};

I know that I can assign VAL a value in the class declaration:

class A
{
public:
static const int VAL = 3;
};

or in the CPP file:

const int A::VAL = 3;

But I would like to read the value in from a data file. I have a function now, let’s call it F() which reads in the value I want:

void F()
{
int value = ReadValueFromDataFile();

//But I can't do this:
const int A::VAL = value; //member cannot be defined in the current scope
}

How can I assign the value of VAL based on a value read in from a data file?

Answer 1

At their definition (not their declaration) initialize the variables with the return value of a function call.

#include <fstream>
#include <iostream>

class A
{
public:
static const int VAL1;
static const int VAL2;
};

int F(const char*);

// If you need to separate .H from .CPP, put the lines above
// in the .H, and the lines below in a .CPP

const int A::VAL1 = F("1.txt");
const int A::VAL2 = F("2.txt");

int F(const char* filename)
{
  std::ifstream file(filename);
  int result = 0;
  file >> result;
  return result;
}

int main () {
  std::cout << A::VAL1 << " " << A::VAL2 << "\n";
}