How to initialize a static variable with another static variable? - c++

Question

Static1.hpp
#include <string>
class Static1
{
public:
static const std::string my_string;
};
Static1.cpp
#include "Static1.hpp"
const std::string Static1::my_string = "aaa";
Static2.hpp
#include <string>
class Static2
{
public:
static const std::string my_string;
};
Static2.cpp
#include "Static2.hpp"
const std::string Static2::my_string = Static1::my_string;
main.cpp
#include "Static2.hpp"
#include <iostream>
int main(argc int, char** argv)
{
cout << to_string(Static2::my_string == "aaa") << endl;
return 0;
}
If I put add_executable(printMyString main.cpp Static2.cpp Static1.cpp) in my CMakeLists.txt, I get
0
while add_executable(printMyString main.cpp Static2.cpp Static1.cpp) gives me the expected behavior of
1
To make my code easier to maintain (so that I don't need to keep track of the order I list my source files), is there any way I can ensure that I get the behavior where Static2::my_string == "aaa"?

Answer 1

You are experiencing effects of a static initialization order fiasco.
The usual work-around is to substitute your static variables with functions that have a static variable in the scope, initialize, and return it.
Here is how it could be done for your example: Live Example (order1)
Live Example (order2)
class Static1
{
public:
static std::string my_string();
};
...
std::string Static1::my_string()
{
static const std::string my_string = "aaa";
return my_string;
}
...
class Static2
{
public:
static std::string my_string();
};
...
std::string Static2::my_string()
{
static const std::string my_string = Static1::my_string();
return my_string;
}
...
std::cout << std::to_string(Static2::my_string() == "aaa") << std::endl;