C++20 support

Makefile.linux

@@ -23,10 +23,12 @@ else ifeq ($(shell expr match ${CXXVER} "[5-6]"),1) # gcc 5 - 6
 else ifeq ($(shell expr match ${CXXVER} "[7-9]"),1) # gcc 7 - 9
 	NEEDED_CXXFLAGS += -std=c++17
 	LDLIBS = -latomic
-else ifeq ($(shell expr match ${CXXVER} "1[0-9]"),2) # gcc 10+
-#	NEEDED_CXXFLAGS += -std=c++20
+else ifeq ($(shell expr match ${CXXVER} "10"),2) # gcc 10
 	NEEDED_CXXFLAGS += -std=c++17
 	LDLIBS = -latomic
+else ifeq ($(shell expr match ${CXXVER} "1[1-9]"),2) # gcc 11+
+	NEEDED_CXXFLAGS += -std=c++20
+	LDLIBS = -latomic
 else # not supported
 $(error Compiler too old)
 endif

build/CMakeLists.txt

@@ -157,18 +157,21 @@ else()
   set(CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS_MINSIZEREL} -ffunction-sections -fdata-sections")
   set(CMAKE_EXE_LINKER_FLAGS_MINSIZEREL "-Wl,--gc-sections") # -flto is added from above
 
-  # check for c++17 & c++11 support
+  # check for с++20 & c++17 & c++11 support
   include(CheckCXXCompilerFlag)
 
+  CHECK_CXX_COMPILER_FLAG("-std=c++20" CXX20_SUPPORTED)
   CHECK_CXX_COMPILER_FLAG("-std=c++17" CXX17_SUPPORTED)
   CHECK_CXX_COMPILER_FLAG("-std=c++11" CXX11_SUPPORTED)
 
-  if(CXX17_SUPPORTED)
+  if(CXX20_SUPPORTED)
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++20")
+  elseif(CXX17_SUPPORTED)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17")
   elseif(CXX11_SUPPORTED)
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
   else()
-    message(SEND_ERROR "C++17 nor C++11 standard not seems to be supported by compiler. Too old version?")
+    message(SEND_ERROR "C++20 nor C++17 nor C++11 standard not seems to be supported by compiler. Too old version?")
   endif()
 endif()
 

libi2pd/FS.cpp

@@ -252,8 +252,12 @@ namespace fs {
 		std::error_code ec;
 		auto t = std::filesystem::last_write_time (path, ec);
 		if (ec) return 0;
-		auto sctp = std::chrono::time_point_cast<std::chrono::system_clock::duration>(
+#if __cplusplus >= 202002L // C++ 20 or higher
+		const auto sctp = std::chrono::clock_cast<std::chrono::system_clock>(t);
+#else		
+		const auto sctp = std::chrono::time_point_cast<std::chrono::system_clock::duration>(
 		    t - decltype(t)::clock::now() + std::chrono::system_clock::now());
+#endif		
    		return std::chrono::system_clock::to_time_t(sctp);	
 #else		
 		boost::system::error_code ec;