c++ 初始化静态static成员变量或static复合成员变量

https://stackoverflow.com/questions/185844/how-to-initialize-private-static-members-in-c

https://stackoverflow.com/questions/1197106/static-constructors-in-c-i-need-to-initialize-private-static-objects

One idiom was proposed at: https://stackoverflow.com/a/27088552/895245 but here goes a cleaner version that does not require creating a new method per member, and a runnable example:

#include <cassert>
#include <vector>

// Normally on the .hpp file.
class MyClass {
public:
    static std::vector<int> v, v2;
    static struct _StaticConstructor {
        _StaticConstructor() {
            v.push_back(1);
            v.push_back(2);
            v2.push_back(3);
            v2.push_back(4);
        }
    } _staticConstructor;
};

// Normally on the .cpp file.
std::vector<int> MyClass::v;
std::vector<int> MyClass::v2;
// Must come after every static member.
MyClass::_StaticConstructor MyClass::_staticConstructor;

int main() {
    assert(MyClass::v[0] == 1);
    assert(MyClass::v[1] == 2);
    assert(MyClass::v2[0] == 3);
    assert(MyClass::v2[1] == 4);
}

GitHub upstream.

Tested with g++ -std=c++11 -Wall -Wextra, GCC 7.3, Ubuntu 18.04.