Why doesn't the order of methods in a class matter in C++?

Question

I have been programming in C++ for quite some time and I never thought about this until today.

Consider the following code:

struct foo
{
  // compiles fi         


        

Answer 1

For the most part, a C++ file is parsed top-to-bottom, so entities must be declared before they are used.

In your class, bar2 and b are invalid because they both make use of my_int_type, which has not yet been declared.

One exception to the "top-to-bottom" parsing rule is member functions that are defined inside the definition of their class. When such a member function definition is parsed, it is parsed as if it appeared after the definition of the class. This is why your usage of my_int_type in bar is valid.

Effectively, this:

struct foo
{
    void bar()
    {
        my_int_type b;
    }

    typedef int my_int_type;
};

is the same as:

struct foo
{
    void bar();

    typedef int my_int_type;
};

inline void foo::bar()
{
    my_int_type b;
}