Question

I’m not sure how to order my functions in C++. In C, I simply placed a function that uses another function below that function, as closely as possible – that’s pretty common. Like this:

void bar()
{
}

void foo()
{
    bar();
}

However, in C++, there are several types of functions:

• Free functions
• Private member functions
• Public member functions
• Static member functions

I’m currently making my function order dependent on how they are ordered in the .hpp file, e.g.:

class Foo_bar {
public:
    Foo_bar();
    void foo();
private:
    int some_member;
    void bar();

But now, if the constructor uses foo() or bar(), these will be below the constructor in the source file, inconsistent with my usual ordering. I could of course reorder my header to take account of that:

class Foo_bar {
private:
    int some_member;
    void bar();

public:
    void foo();
    Foo_bar();

But I think that’s a mess.

Furthermore, in Java, the opposite to my first example seems to be common:

void foo()
{
    bar();
}

void bar()
{
}

That’s probably due to the top-down thinking common in OOP, in contrast to the bottom-up thinking common in procedural/functional programming. However, with free functions that don’t have prototypes, this top-down style is not possible.

Is it even possible to order functions in C++ in a consistent way?

Answer 1

It’s possible. You have to use forward declaration.

Declare a function before defining it, and other functions will see it without problem even if they are defined before.

So, you should be able to do this in C++:

void bar();  // forward declaration; note that function bar isn't defined yet

void foo()
{
    bar();   // foo knows that bar is declared, so it will search for bar's definition
}

void bar()   // here bar is defined, so foo will use this when needed
{
}