C++ Static members of a class are initialized after constructor - c++

Question

I have a problem with static members of a class not being initialized before the constructor. Am i doing something wrong? Is it a bug in G++ ?
Any workarounds?
g++ --version : (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4
I am also using Eclipse as my IDE, but i just copy the static lib headers to /usr/include/StaticTestLib/InitTest.h and the library to /usr/lib/x86_64-linux-gnu/libStaticTestLib.a
Note this only happens if the object that holds the data is defined before main and the class is in a Static Library.
Static library header (the static library itself is named StaticTestLib):
InitTest.h
#include <iostream>
namespace StaticTestLib {
class notifier_header{
public:
notifier_header(){
std::cout<<"static var init"<<std::endl;
}
};
class InitTest {
public:
static notifier_header _header_notifier;
InitTest();
virtual ~InitTest();
};
}
Static library source file:
InitTest.cpp
#include "InitTest.h"
namespace StaticTestLib {
notifier_header InitTest::_header_notifier;
class notifier_cpp{
public:
notifier_cpp(){
std::cout<<"code before constructor"<<std::endl;
}
}_notifier_in_cpp;
InitTest::InitTest() {
std::cout<<"constructor"<<std::endl;
}
InitTest::~InitTest() {
std::cout<<"destructor"<<std::endl;
}
}
This program:
StaticTest.cpp
#include <iostream>
#include <StaticTestLib/InitTest.h>
StaticTestLib::InitTest test;
int main() {
std::cout << "program main" << std::endl;
std::cout << "program end" << std::endl;
return 0;
}
… outputs:
constructor
static var init
code before constructor
program main
program end
destructor
But this program:
#include <iostream>
#include <StaticTestLib/InitTest.h>
int main() {
std::cout << "program main" << std::endl;
StaticTestLib::InitTest test;
std::cout << "program end" << std::endl;
return 0;
}
… outputs:
static var init
code before constructor
program main
contructor
program end
destructor

Answer 1

My guess is that this is related to the order of static objects initialisation in different compilation units being undefined.
The second code snippet where you create a test object in your main is easy to explain. Static initialisation will always happen before any code is executed, so by the time you enter main, your notifier_header object is definitely created.
Now, when you create your test before main, you have two static objects. notifier_header object does not depend on your InitTest: it is scoped within that class, but it is stored in static memory. You seem to reference the notifier_header in your InitTest.cpp, which is a different compilation unit to main. A compiler is free to do static allocations in any order for those two units, provided that there is no interdependencies.
If your constructor depended on notifier_header, you could use it as a singleton. Create a function that returns an instance of a static object (headerInstance in the example below), and upon its call, the object will be created:
#include <iostream>
namespace StaticTestLib {
class notifier_header{
public:
notifier_header(){
std::cout<<"static var init"<<std::endl;
}
};
class InitTest {
public:
InitTest();
virtual ~InitTest();
notifier_header& headerInstance();
};
}
Static library source file (InitTest.cpp)
#include "InitTest.h"
namespace StaticTestLib {
class notifier_cpp{
public:
notifier_cpp(){
std::cout<<"code before constructor"<<std::endl;
}
}_notifier_in_cpp;
InitTest::InitTest() {
headerInstance();
std::cout<<"constructor"<<std::endl;
}
InitTest::~InitTest() {
std::cout<<"destructor"<<std::endl;
}
notifier_header& InitTest::headerInstance() {
static notifier_header _header_notifier; // will only be constructed once
return _header_notifier;
}
}
The output I get:
static var init
constructor
code before constructor
program main
program end
destructor