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--- howto:module_std_gcc15 [2025-03-08 16:28] – gelöscht - Externe Bearbeitung (Unbekanntes Datum) 127.0.0.1
+++ howto:module_std_gcc15 [2025-03-08 16:34] (aktuell) – rrichter
@@ Zeile 1: / Zeile 1: @@
+====== How to use C++ module std in GNU g++-15 ======
+Modules with g++15 HEAD, CMake and Ninja under Windows 10. Warning: This is experimental.
+A small demo project. Available on [[https://github.com/rene-richter/cpp_module_std_cmake_gcc15HEAD|Github]].
+How to build and execute:
+<code>
+cd build
+cmake -G Ninja
+ninja
+demo
+</code>
+Prerequisites:
+  * GCC 15 HEAD https://www.equation.com gcc-15-2024-1215-64.exe
+  * CMake 3.31.3
+  * Ninja 1.12.1
+Limitations (at the time of writing, 2025-02-21):
+  * CMake supports C++ modules for Ninja generator only
+  * CMake tells Ninja nothing about module std. Hack: extra library ''%%module_std%%'' in ''%%CMakeList.txt%%''.
+Some lines in source file ''%%gnu/std.cc%%'' (copied from ''%%MinGW/include/c++/15.0.0/bits/std.cc%%'') had to be commented out:
+<code cpp>
+// using std::aligned_alloc;
+// using std::timespec;
+// using std::timespec_get;
+// using std::mbrtoc8;
+// using std::c8rtomb;
+</code>
+Sadly, newer weekly build compiler ''%%https://www.equation.com/ftpdir/gcc-15-20250202-64.exe%%'' resulted in compilation error: ''%%exposes TU-local entity%%''. :-(
+==== CMake ====
+<code>
+cmake_minimum_required(VERSION 3.31)
+project(
+    compile_with_module_std
+    VERSION 0.0.1
+    LANGUAGES CXX)
+# temporary hack for GCC g++15.0 HEAD https://www.equation.com gcc-15-20241215-64.exe
+# to remove when g++ & CMake know about module std
+add_library(module_std)
+target_sources(module_std
+    PUBLIC
+        FILE_SET CXX_MODULES FILES
+            gnu/std.cc # modified from MinGW\include\c++\15.0.0\bits\std.cc
+)
+target_compile_features(module_std PUBLIC cxx_std_26)
+# also to remove (see below):
+# target_link_libraries(...XYZ... PRIVATE module_std)
+# another hack for advanced features like std::print(), std::stacktrace, etc in g++14 and g++15.0 HEAD:
+# target_link_libraries(...XYZ... PRIVATE stdc++exp)
+add_library(my_module)
+target_sources(my_module
+    PUBLIC
+        FILE_SET CXX_MODULES FILES
+            src/my_module.cpp
+)
+target_compile_features(my_module PUBLIC cxx_std_26)
+target_link_libraries(my_module PRIVATE module_std)
+add_executable(demo src/demo.cpp)
+target_compile_features(demo PUBLIC cxx_std_26)
+target_link_libraries(demo PRIVATE module_std)
+target_link_libraries(demo PRIVATE my_module)
+target_link_libraries(demo PRIVATE stdc++exp)
+</code>
+==== C++ code ====
+Modular ''%%src/my_module.cpp%%''
+<code cpp>
+export module my_first_module;
+import std;
+export namespace something
+{
+std::string hello(std::string name)
+{
+    return "Hello, " + name + '!';
+}
+} // end namespace something
+</code>
+used in ''%%demo.cpp%%'':
+<code cpp>
+import std;
+import my_first_module;
+int main()
+{
+    std::println("{}", something::hello("modules"));
+}
+</code>