a.cpp

#include "a.h"
#include <iostream>
static int _inited = []() -> int {
  std::cout << "NS: " << NSFoo() << ", Static: " << StaticFoo()
            << ", Inline: " << InlineFoo() << ", Cls: " << Foo::ClsFoo()
            << ", Weak: " << WeakSymbFoo() << std::endl;
  return 0;
}();⏎

a.h

#pragma once
#include <iostream>
namespace {
int *NSFoo() {
  static int val;
  return &val;
}
} // namespace

static int *StaticFoo() {
  static int val;
  return &val;
}

inline int *InlineFoo() {
  static int val;
  return &val;
}

class Foo {
public:
  static int *ClsFoo() {
    static int val;
    return &val;
  }
};
int *WeakSymbFoo() __attribute__((weak));
int *WeakSymbFoo() {
  static int val;
  return &val;
}⏎

build.sh

#!/bin/bash
clang++ -std=c++20 *.cpp -o a.out

main.cpp

#include "a.h"
#include <iostream>
static int _inited = []() -> int {
  std::cout << "NS: " << NSFoo() << ", Static: " << StaticFoo()
            << ", Inline: " << InlineFoo() << ", Cls: " << Foo::ClsFoo()
            << ", Weak: " << WeakSymbFoo() << std::endl;
  return 0;
}();

int main() {}⏎

output.txt

NS: 0x1018c60e0, Static: 0x1018c60e4, Inline: 0x1018c60d0, Cls: 0x1018c60d4, Weak: 0x1018c60d8
NS: 0x1018c60f0, Static: 0x1018c60f4, Inline: 0x1018c60d0, Cls: 0x1018c60d4, Weak: 0x1018c60d8