Can you define variables in a class/struct?

[GreatBlitz]

I used to own the C++ Primer 4th Edition which stated that definitions should not appear in headers. But the new edition has this:

#ifndef SALES_DATA_H
#define SALES_DATA_H
#include <string>
struct Sales_data {
std::string bookNo;
unsigned units_sold = 0;
double revenue = 0.0;
};
#endif 

There are definitions in the header( units_sold = 0 ). So is this contradictory information?

[JLBorges]

> There are definitions in the header( units_sold = 0 ). So is this contradictory information?

These are default member initialisers. They came with C++11.

For more information, see: 'Member initialization' in http://en.cppreference.com/w/cpp/language/data_members

[GreatBlitz]

These are default member initialisers. They came with C++11.

So what is the difference between default member initialisers and normal definitons?

Also, am I allowed to define methods in classes/structs/headers? (still don't understand the difference)

[JLBorges]

> So what is the difference between default member initialisers and normal definitons?

1.

If a member has a default member initializer and also appears in the member initialization list in a constructor, the default member initializer is ignored. http://en.cppreference.com/w/cpp/language/data_members

2. Only a brace-or-equal-initialiser is accepted as a default member initialiser