basic_demo.cpp:13:12: error: 'template<class> class vdk::signal' conflicts with a previous declaration

[anb0s]

I'm facing compile errors with MInGW GCC 9.2 at Windows in basic_demo.cpp, cross_thread_calls.cpp and cross_thread_calls.cpp, because using vdk::signal conflicts then with x86_64-w64-mingw32/include/signal.h:60:24: note: previous declaration 'void (* signal(int, __p_sig_fn_t))(int)'

---------- ERRORS occurred while compiling file D:\git\s7p\work3\s7p.base\vdk\signals-master\demo\basic_demo.cpp
D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/basic_demo.cpp:13:12: error: 'template<class> class vdk::signal' conflicts with a previous declaration
   13 | using vdk::signal;
      |            ^~~~~~
In file included from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/x86_64-w64-mingw32/include/pthread.h:68,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/x86_64-w64-mingw32/bits/gthr-default.h:35,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/x86_64-w64-mingw32/bits/gthr.h:148,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/ext/atomicity.h:35,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/bits/ios_base.h:39,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/ios:42,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/ostream:38,
                 from D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/include/c++/9.2.0/iostream:39,
                 from D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/demo.h:10,
                 from D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/basic_demo.cpp:7:
D:\git\s7p\work3\s7p.tools/win64_gcc_mingw64_9.2.0/x86_64-w64-mingw32/include/signal.h:60:24: note: previous declaration 'void (* signal(int, __p_sig_fn_t))(int)'
   60 |   __p_sig_fn_t __cdecl signal(int _SigNum,__p_sig_fn_t _Func);
      |                        ^~~~~~
D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/basic_demo.cpp: In function 'void signals_basic_demo()':
D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/basic_demo.cpp:55:12: error: expected primary-expression before 'void'
   55 |     signal<void(int)> sig;
      |            ^~~~
D:/git/s7p/work3/s7p.base/vdk/signals-master/demo/basic_demo.cpp:58:5: error: 'sig' was not declared in this scope
   58 |     sig.connect(function);
      |     ^~~

After removing using vdk::signal and adding vdk:: to signal<void(const string &)> sig; it works then.

[vdksoft]

Hi, thanks for pointing that out. In fact, this error is weird: signal mentioned in the error message is supposed to be in std namespace. I don't see how they may conflict. Anyway, I will just remove using declarations in demo files to fix the problem.

[anb0s]

Hi, thanks for pointing that out. In fact, this error is weird: signal mentioned in the error message is supposed to be in std namespace. I don't see how they may conflict. Anyway, I will just remove using declarations in demo files to fix the problem.

It looks like it comes from demo.h:10 --> iostream:39 --> ... --> pthread.h:68 --> signal.h:60, so here we have the declaration of void (* signal(int, __p_sig_fn_t))(int) without any std namespace etc., because it's C / POSIX and not C++.

I've also no idea how to avoid it and created an PR as you also described.

[zhengzubing]

I'm facing the same compile errors with CLion at MacOS sequoia

/Users/zhengzubing/CLionProjects/signals/demo/track_objects.cpp:15:12: error: target of using declaration conflicts with declaration already in scope
   15 | using vdk::signal;
      |            ^
/Users/zhengzubing/CLionProjects/signals/src/signals.h:19:7: note: target of using declaration
   19 | class signal;
      |       ^
/Library/Developer/CommandLineTools/SDKs/MacOSX15.5.sdk/usr/include/sys/signal.h:390:7: note: conflicting declaration
  390 | void(*signal(int, void (*)(int)))(int);

After removing using vdk::signal and adding vdk:: to signal<void(const string &)> sig; it works then.