Require C++23.

CMakeLists.txt

@@ -24,12 +24,12 @@ set (CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 enable_language (CXX)
 if (MSVC)
-  set (CMAKE_CXX_STANDARD 20)
+  set (CMAKE_CXX_STANDARD 23)
   if (CMAKE_VS_PLATFORM_NAME MATCHES "ARM")
     set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /EHsc")
   endif ()
 else ()
-  set (CMAKE_CXX_STANDARD 20)
+  set (CMAKE_CXX_STANDARD 23)
 endif ()
 set (CMAKE_CXX_STANDARD_REQUIRED ON)
 set (CMAKE_CXX_EXTENSIONS ON)

Makefile.in

@@ -1086,7 +1086,7 @@ EXEEXT = @EXEEXT@
 FGREP = @FGREP@
 FILECMD = @FILECMD@
 GREP = @GREP@
-HAVE_CXX20 = @HAVE_CXX20@
+HAVE_CXX23 = @HAVE_CXX23@
 INSTALL = @INSTALL@
 INSTALL_DATA = @INSTALL_DATA@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@

configure

@@ -724,7 +724,7 @@ USE_LOG4CPLUS_EXPORT_SYMBOLS_REGEX_TRUE
 LOG4CPLUS_AIX_XLC_LDFLAGS
 GREP
 SED
-HAVE_CXX20
+HAVE_CXX23
 CXXCPP
 am__fastdepCXX_FALSE
 am__fastdepCXX_TRUE
@@ -6684,17 +6684,17 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
 
 
-  ax_cxx_compile_alternatives="20"    ax_cxx_compile_cxx20_required=true
+  ax_cxx_compile_alternatives="23 2b"    ax_cxx_compile_cxx23_required=true
   ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'
 ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
   ac_success=no
 
-      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++20 features by default" >&5
-printf %s "checking whether $CXX supports C++20 features by default... " >&6; }
-if test ${ax_cv_cxx_compile_cxx20+y}
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++23 features by default" >&5
+printf %s "checking whether $CXX supports C++23 features by default... " >&6; }
+if test ${ax_cv_cxx_compile_cxx23+y}
 then :
   printf %s "(cached) " >&6
 else case e in #(
@@ -7516,29 +7516,55 @@ namespace cxx20
 
 
 
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202302L && !defined _MSC_VER
+
+#error "This is not a C++23 compiler"
+
+#else
+
+#include <version>
+
+namespace cxx23
+{
+
+// As C++23 supports feature test macros in the standard, there is no
+// immediate need to actually test for feature availability on the
+// Autoconf side.
+
+}  // namespace cxx23
+
+#endif  // __cplusplus < 202302L && !defined _MSC_VER
+
+
+
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"
 then :
-  ax_cv_cxx_compile_cxx20=yes
+  ax_cv_cxx_compile_cxx23=yes
 else case e in #(
-  e) ax_cv_cxx_compile_cxx20=no ;;
+  e) ax_cv_cxx_compile_cxx23=no ;;
 esac
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext ;;
 esac
 fi
-{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_cxx_compile_cxx20" >&5
-printf "%s\n" "$ax_cv_cxx_compile_cxx20" >&6; }
-    if test x$ax_cv_cxx_compile_cxx20 = xyes; then
+{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $ax_cv_cxx_compile_cxx23" >&5
+printf "%s\n" "$ax_cv_cxx_compile_cxx23" >&6; }
+    if test x$ax_cv_cxx_compile_cxx23 = xyes; then
       ac_success=yes
     fi
 
     if test x$ac_success = xno; then
     for alternative in ${ax_cxx_compile_alternatives}; do
       switch="-std=gnu++${alternative}"
-      cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx20_$switch" | sed "$as_sed_sh"`
-      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++20 features with $switch" >&5
-printf %s "checking whether $CXX supports C++20 features with $switch... " >&6; }
+      cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx23_$switch" | sed "$as_sed_sh"`
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++23 features with $switch" >&5
+printf %s "checking whether $CXX supports C++23 features with $switch... " >&6; }
 if eval test \${$cachevar+y}
 then :
   printf %s "(cached) " >&6
@@ -8363,6 +8389,32 @@ namespace cxx20
 
 
 
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202302L && !defined _MSC_VER
+
+#error "This is not a C++23 compiler"
+
+#else
+
+#include <version>
+
+namespace cxx23
+{
+
+// As C++23 supports feature test macros in the standard, there is no
+// immediate need to actually test for feature availability on the
+// Autoconf side.
+
+}  // namespace cxx23
+
+#endif  // __cplusplus < 202302L && !defined _MSC_VER
+
+
+
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"
 then :
@@ -8392,9 +8444,9 @@ printf "%s\n" "$ac_res" >&6; }
     if test x$ac_success = xno; then
                 for alternative in ${ax_cxx_compile_alternatives}; do
       for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
-        cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx20_$switch" | sed "$as_sed_sh"`
-        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++20 features with $switch" >&5
-printf %s "checking whether $CXX supports C++20 features with $switch... " >&6; }
+        cachevar=`printf "%s\n" "ax_cv_cxx_compile_cxx23_$switch" | sed "$as_sed_sh"`
+        { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++23 features with $switch" >&5
+printf %s "checking whether $CXX supports C++23 features with $switch... " >&6; }
 if eval test \${$cachevar+y}
 then :
   printf %s "(cached) " >&6
@@ -9219,6 +9271,32 @@ namespace cxx20
 
 
 
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202302L && !defined _MSC_VER
+
+#error "This is not a C++23 compiler"
+
+#else
+
+#include <version>
+
+namespace cxx23
+{
+
+// As C++23 supports feature test macros in the standard, there is no
+// immediate need to actually test for feature availability on the
+// Autoconf side.
+
+}  // namespace cxx23
+
+#endif  // __cplusplus < 202302L && !defined _MSC_VER
+
+
+
 _ACEOF
 if ac_fn_cxx_try_compile "$LINENO"
 then :
@@ -9254,19 +9332,19 @@ ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
-  if test x$ax_cxx_compile_cxx20_required = xtrue; then
+  if test x$ax_cxx_compile_cxx23_required = xtrue; then
     if test x$ac_success = xno; then
-      as_fn_error $? "*** A compiler with support for C++20 language features is required." "$LINENO" 5
+      as_fn_error $? "*** A compiler with support for C++23 language features is required." "$LINENO" 5
     fi
   fi
   if test x$ac_success = xno; then
-    HAVE_CXX20=0
-    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: No compiler with C++20 support was found" >&5
-printf "%s\n" "$as_me: No compiler with C++20 support was found" >&6;}
+    HAVE_CXX23=0
+    { printf "%s\n" "$as_me:${as_lineno-$LINENO}: No compiler with C++23 support was found" >&5
+printf "%s\n" "$as_me: No compiler with C++23 support was found" >&6;}
   else
-    HAVE_CXX20=1
+    HAVE_CXX23=1
 
-printf "%s\n" "#define HAVE_CXX20 1" >>confdefs.h
+printf "%s\n" "#define HAVE_CXX23 1" >>confdefs.h
 
   fi
 

configure.ac

@@ -179,7 +179,7 @@ AC_PROG_CXX
 AC_PROG_CXXCPP
 AC_LANG([C++])
 
-AX_CXX_COMPILE_STDCXX([20],[],[mandatory])
+AX_CXX_COMPILE_STDCXX([23],[],[mandatory])
 
 AS_VAR_APPEND([CPPFLAGS], [" -D_GNU_SOURCE=1"])
 

include/Makefile.in

@@ -229,7 +229,7 @@ EXEEXT = @EXEEXT@
 FGREP = @FGREP@
 FILECMD = @FILECMD@
 GREP = @GREP@
-HAVE_CXX20 = @HAVE_CXX20@
+HAVE_CXX23 = @HAVE_CXX23@
 INSTALL = @INSTALL@
 INSTALL_DATA = @INSTALL_DATA@
 INSTALL_PROGRAM = @INSTALL_PROGRAM@

m4/ax_cxx_compile_stdcxx.m4

@@ -52,7 +52,8 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
   m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
         [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
         [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
-        [$1], [20], [ax_cxx_compile_alternatives="20"],
+        [$1], [20], [ax_cxx_compile_alternatives="20 2a"],
+        [$1], [23], [ax_cxx_compile_alternatives="23 2b"],
         [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
   m4_if([$2], [], [],
         [$2], [ext], [],
@@ -177,6 +178,16 @@ m4_define([_AX_CXX_COMPILE_STDCXX_testbody_20],
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_20
 )
 
+dnl  Test body for checking C++23 support
+
+m4_define([_AX_CXX_COMPILE_STDCXX_testbody_23],
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_20
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_23
+)
+
 
 dnl  Tests for new features in C++11
 
@@ -1007,3 +1018,33 @@ namespace cxx20
 #endif  // __cplusplus < 202002L && !defined _MSC_VER
 
 ]])
+
+
+dnl  Tests for new features in C++23
+
+m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_23], [[
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus < 202302L && !defined _MSC_VER
+
+#error "This is not a C++23 compiler"
+
+#else
+
+#include <version>
+
+namespace cxx23
+{
+
+// As C++23 supports feature test macros in the standard, there is no
+// immediate need to actually test for feature availability on the
+// Autoconf side.
+
+}  // namespace cxx23
+
+#endif  // __cplusplus < 202302L && !defined _MSC_VER
+
+]])