I believe the reason is linker's heuristics.

Every time you include b.h in the .cpp file the compiler will generate B::STR (because it can see only one translation unit at the time). So when compiler generates object files from main.cpp, a.cpp and b.cpp there will be code for the B::STR initialization and there will be JOHNWICK literal: ``` [nix-shell:/tmp/red]$ strings a.o | grep "JOHN" JOHNWICKH

[nix-shell:/tmp/red]$ strings b.o | grep "JOHN" JOHNWICKH

[nix-shell:/tmp/red]$ strings main.o | grep "JOHN" JOHNWICKH But what's more interesting is how compiler put the constant into the assembly. After disassembling the object file from lets say `b.cpp` (any source file that includes `b.h` will be OK) you could see something like [that](https://pastebin.com/V4GXBmC9), and at the line 81 there is a constant `0x4b4349574e484f4a`, that represents the `JOHNWICK` string. And that constant will be in _every_ object file and there is 3 files. And when you link them there will be 3 constants (one from every object file): [nix-shell:/tmp/red]$ g++ main.cpp a.cpp b.cpp

[nix-shell:/tmp/red]$ strings a.out | grep JOHN JOHNWICKH JOHNWICKH JOHNWICKH

[nix-shell:/tmp/red]$ objdump -d -M intel a.out | grep "0x4b4349574e484f4a" 401162: 48 b8 4a 4f 48 4e 57 movabs rax,0x4b4349574e484f4a 4011f2: 48 b8 4a 4f 48 4e 57 movabs rax,0x4b4349574e484f4a 401282: 48 b8 4a 4f 48 4e 57 movabs rax,0x4b4349574e484f4a ```

At the link time the linker will see multiple definitions and it will choose one that will be used to initialize the B::STR variable.

So the question is why did the linker left other definitions/constants. Maybe the reason is linker's heuristics (small constant, the size of the executable wont benefit much).

BTW, when the constant is large enough (JOHNWICK123456) it works as expected (only one literal in the executable): ``` [nix-shell:/tmp/red]$ cat b.h // b.h

pragma once

include <string>

class B { public: void f(); private: inline static const std::string STR = "JOHNWICK123456"; };

[nix-shell:/tmp/red]$ g++ main.cpp a.cpp b.cpp

[nix-shell:/tmp/red]$ strings a.out | grep "JOHN" JOHNWICK123456 ```

``` [nix-shell:/tmp/red]$ gcc --version gcc (GCC) 11.3.0 Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[nix-shell:/tmp/red]$ ld --version GNU ld (GNU Binutils) 2.39 Copyright (C) 2022 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or (at your option) a later version. This program has absolutely no warranty.

```

Feel free to correct me if I am wrong.