Hello, I work on Ubuntu wih gcc 15. I searched for specific information on module mapper file, but couldn't find much on the Internet... I read the official document, also the documentation, some links like https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Module-Mapper.html, but still cannot understand properly this issue. Some people also mentioned a g++-mapper-server, but I couldn't find it on gcc-15 on ubuntu (https://github.com/michigan-musicer/modules-demo). It seems the same problem as this ( https://github.com/msys2/MINGW-packages/issues/12797), but it didn't seem to be solved, although old. Sorry if that's documented somewhere. I manage to make the example work with CMake 4.0, but cannot do it manually with mapper file. I have two files: main.cpp, that does "import std; import hello;" and hello.cppm, which does "export module hello;" and "import std;" These are organized as example/hello-world/main.cpp and example/hello-world/hello.cppm, and then, I manage to compile std module and generate example/hello-world/gcm.cache/std.gcm. I have a limitation that I cannot run g++ command directly inside the folder containing gcm.cache, so I created a example/hello-world/gcm.cache/mapper.txt file with the following content: std gcm.cache/std.gcm Then, I try to compile as follows (trying to generate hello.gcm): g++-15 - -fmodules '-std=c++23' -c example/hello-world/hello.cppm -fmodule-mapper=example/hello-world/mapper.txt But then, it complains of 'hello' module: example/hello-world/hello.cppm:3:8: fatal error: unknown compiled module interface: no such module 3 | export module hello; If I go inside the folder example/hello-world/ and run g++ command with module-mapper, then it works fine, because it already searches for gcm.cache/ folder automatically... however, my process cannot run inside that folder, so do I really need a module mapper file or something else? Complete files: main.cc // main.cc import hello; import std; int main() { say_hello("world"); return 0; } hello.cppm // hello.cppm export module hello; import std; export inline void say_hello(std::string_view const &name) { std::cout << "Hello " << name << "!\n"; } Best regards and sorry for the inconvenience. Igor Machado
