C++ Coding Standard

Rule: OLC#012

Synopsis:	Do not initialise static variables with other (external) static variables
Language:	C++
Severity Level:	6
Category:	Object Life Cycle

Description:

The standard states that static variables are zero initialised before their first use. The order of initialization is not defined across compilation units. So when a static variable is being initialized with another (external) static variable it might be initialised with only the zero initialised value instead of the programmer intended initialised value.

Violating example:

extern int i;
 
class A
{
public:
    // error: i might be initialised with 0 or the intended value
    static int j = i;
};

Non-violating example:

int i = 5;

class A
{
public:
    static int j = i;
};