implement test for C++11 and document it

cmake/CMakeLists.txt

@@ -52,10 +52,17 @@ check_for_autogen_files(${LAMMPS_SOURCE_DIR})
 include(CheckCCompilerFlag)
 include(CheckIncludeFileCXX)
 
-if (${CMAKE_CXX_COMPILER_ID} STREQUAL "Intel")
+if(${CMAKE_CXX_COMPILER_ID} STREQUAL "Intel")
   set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -restrict")
 endif()
 
+option(DISABLE_CXX11_REQUIREMENT "Disable check that requires C++11 for compiling LAMMPS" OFF)
+if(DISABLE_CXX11_REQUIREMENT)
+  add_definitions(-DLAMMPS_CXX98)
+else()
+  set(CMAKE_CXX_STANDARD 11)
+endif()
+
 # GNU compiler features
 if (${CMAKE_CXX_COMPILER_ID} STREQUAL "GNU")
   option(ENABLE_COVERAGE "Enable code coverage" OFF)

doc/src/Build_settings.txt

@@ -12,6 +12,7 @@ Optional build settings :h3
 LAMMPS can be built with several optional settings.  Each sub-section
 explain how to do this for building both with CMake and make.
 
+"C++11 standard compliance test"_#cxx11 when building all of LAMMPS
 "FFT library"_#fft for use with the "kspace_style pppm"_kspace_style.html command
 "Size of LAMMPS data types"_#size
 "Read or write compressed files"_#gzip
@@ -23,6 +24,28 @@ explain how to do this for building both with CMake and make.
 
 :line
 
+C++11 standard compliance test :h4(cxx11)
+
+The LAMMPS developers plan to transition to make the C++11 standard the
+minimum requirement for compiling LAMMPS.  Currently this only applies to
+some packages like KOKKOS while the rest aims to be compatible with the C++98
+standard.  Most currently used compilers are compatible with C++11; some need
+to set extra flags to switch.  To determine the impact of requiring C++11,
+we have added a simple compliance test to the source code, that will cause
+the compilation to abort, if C++11 compliance is not available or enabled.
+To bypass this check, you need to change a setting in the makefile or
+when calling CMake.
+
+[CMake variable]:
+
+-D DISABLE_CXX11_REQUIREMENT=yes
+
+[Makefile.machine setting]:
+
+LMP_INC = -DLAMMPS_CXX98
+
+:line
+
 FFT library :h4,link(fft)
 
 When the KSPACE package is included in a LAMMPS build, the

src/MAKE/Makefile.mpi

@@ -26,12 +26,12 @@ SHLIBFLAGS =	-shared
 # if you change any -D setting, do full re-compile after "make clean"
 
 # LAMMPS ifdef settings
-# see possible settings in Section 2.2 (step 4) of manual
+# see possible settings in Section 3.5 of the manual
 
-LMP_INC =	-DLAMMPS_GZIP -DLAMMPS_MEMALIGN=64
+LMP_INC =	-DLAMMPS_GZIP -DLAMMPS_MEMALIGN=64  # -DLAMMPS_CXX98
 
 # MPI library
-# see discussion in Section 2.2 (step 5) of manual
+# see discussion in Section 3.4 of the manual
 # MPI wrapper compiler/linker can provide this info
 # can point to dummy MPI library in src/STUBS as in Makefile.serial
 # use -D MPICH and OMPI settings in INC to avoid C++ lib conflicts

src/MAKE/Makefile.serial

@@ -26,12 +26,12 @@ SHLIBFLAGS =	-shared
 # if you change any -D setting, do full re-compile after "make clean"
 
 # LAMMPS ifdef settings
-# see possible settings in Section 2.2 (step 4) of manual
+# see possible settings in Section 3.5 of the manual
 
-LMP_INC =	-DLAMMPS_GZIP -DLAMMPS_MEMALIGN=64
+LMP_INC =	-DLAMMPS_GZIP -DLAMMPS_MEMALIGN=64  # -DLAMMPS_CXX98
 
 # MPI library
-# see discussion in Section 2.2 (step 5) of manual
+# see discussion in Section 3.4 of the manual
 # MPI wrapper compiler/linker can provide this info
 # can point to dummy MPI library in src/STUBS as in Makefile.serial
 # use -D MPICH and OMPI settings in INC to avoid C++ lib conflicts

src/lmptype.h

@@ -28,6 +28,13 @@
 #ifndef LMP_LMPTYPE_H
 #define LMP_LMPTYPE_H
 
+// C++11 check
+#ifndef LAMMPS_CXX98
+#if __cplusplus <= 199711L
+  #error LAMMPS is planning to transition to C++11. Do disable this error please use a C++11 compliant compiler, enable C++11 (or later) compliance, or define LAMMPS_CXX98 in your makefile
+#endif
+#endif
+
 #ifndef __STDC_LIMIT_MACROS
 #define __STDC_LIMIT_MACROS
 #endif