Im am trying to implement a design of a "HasUtility" template class allowing to create templated static member (utilities) and maintening a list of all utilities (base classes)
Here is the code:
StaticUtilityBase.h:
#include <vector>
#include <iostream>
class StaticUtilityBase {
public:
static std::vector<StaticUtilityBase*> all;
StaticUtilityBase() {
all.push_back(this);
printAllState();
}
static void printAllState() {
std::cout << "All size is " << all.size() << ", address is " << &all << std::endl;
}
};
template <typename T> class StaticUtility : public StaticUtilityBase {};
template <typename T> class HasUtility {
public:
static StaticUtility<T> utility;
};
template <typename T> StaticUtility<T> HasUtility<T>::utility;
TemplateUtility.cpp:
#include "StaticUtilityBase.h"
std::vector<StaticUtilityBase*> StaticUtilityBase::all;
and the main:
#include <iostream>
#include "StaticUtilityBase.h"
class A {};
class B {};
int main() {
std::cout << "Initializations done" << std::endl;
StaticUtilityBase::printAllState();
HasUtility<A>::utility; //Tell to the compiler that the static member is used so the constructor
HasUtility<B>::utility; // of utility is used before main execution, during initializations
}
When executing I have the following result:
All size is 1, address is 0x562942baa1f0
All size is 2, address is 0x562942baa1f0
Initializations done
All size is 0, address is 0x562942baa1f0
All size should still be 2 at the end. Looks like "all" is reinitialized after the "utility" members initialization! The address is the same so I think it is the same object. Maybe it has been copied from an empty one?? Any help welcome!
I use gcc and C++17
You are accessing a static object (in this case StaticUtilityBase::all
) from the constructor of a different static object (in this case template <typename T> StaticUtility<T> HasUtility<T>::utility;
).
As there is no ordering guarantee between initialisation of different static objects across translations units what you are trying to do won't work.
See https://en.cppreference.com/w/cpp/language/siof for more information.
And easy way to verify this is to add a second static object to StaticUtilityBase
which prints out when it gets constructed: static int printer = []()->int{std::cout << "Initing StaticUtilityBase\\n"; return 0;}()
static int printer = []()->int{std::cout << "Initing StaticUtilityBase\\n"; return 0;}()
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.