inline variables do not call constructor

[Harris__John]

There appears to be a bug with inline variable initialization.  The following code prints "0".  With gcc, it prints "1".

(ICC) 19.0.0.117 20180804

#include <iostream>

int flag = 0;

class C
{
public:
  C() { ::flag = 1; }
};

class D
{
public:
  static inline C c = C();
};

int main(int, char **)
{
  D d;
  std::cout << ::flag << std::endl;
}
 
 

[jimdempseyatthecove]

This may be a case of vendor dependent behavior between the order of a static constructor and global variable initialization.

Jim Dempsey 

[Harris__John]

Thanks, but the behavior is the same if you assert() or throw() in the constructor.  The constructor does not get called at all...ever.

[jimdempseyatthecove]

Those may be determined at compile time.

Copy the last statement of main, and insert into first statement of the ctor and see what happens. 

[Harris__John]

Strange. If you put the iostream operation in there, it gets run, but if you put throw(0) in the constructor, it doesn't get run...using icpc.

class C
{
public:
  C() { throw(0); }
};

class D
{
public:
  static inline C c = C();
};

int main(int, char **)
{
  D d;
}
 

[Harris__John]

More to the point, this core dumps with a floating point exception, because the unordered_map ctor doesn't get run.  This is how I found the problem:

#include <unordered_map>

class C
{
public:
  C() { m.find(0); }
  static inline std::unordered_map<int,int> m;
};

int main(int, char **)
{
  C c;
  return 0;
}