diff --git a/GNUmakefile b/GNUmakefile
index ee67b93d..b0773609 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -24,6 +24,9 @@ LD      ?= ld
 MDBX_OPTIONS ?= -DNDEBUG=1
 CFLAGS  ?= -O2 -g -Wall -Werror -Wextra -Wpedantic -ffunction-sections -fPIC -fvisibility=hidden -std=gnu11 -pthread -Wno-error=attributes $(CFLAGS_EXTRA)
 # -Wno-tautological-compare
+CXX     ?= g++
+CXXSTD  ?= $(shell PROBE=$$([ -f mdbx.c++ ] && echo mdbx.c++ || echo src/mdbx.c++); for std in gnu++20 c++20 gnu++2a c++2a gnu++17 c++17 gnu++14 c++14 gnu+11 c++11; do $(CXX) -std=$${std} -c $${PROBE} -o /dev/null 2>/dev/null >/dev/null && echo "-std=$${std}" && exit; done)
+CXXFLAGS:= $(CXXSTD) $(filter-out -std=gnu11,$(CFLAGS))
 
 # HINT: Try append '--no-as-needed,-lrt' for ability to built with modern glibc, but then run with the old.
 LIBS    ?= $(shell uname | grep -qi SunOS && echo "-lkstat") $(shell uname | grep -qi -e Darwin -e OpenBSD || echo "-lrt") $(shell uname | grep -qi Windows && echo "-lntdll")
@@ -132,9 +135,6 @@ TEST_ITER  := $(shell $(uname2titer))
 TEST_SRC   := test/osal-$(TEST_OSAL).cc $(filter-out $(wildcard test/osal-*.cc), $(wildcard test/*.cc))
 TEST_INC   := $(wildcard test/*.h)
 TEST_OBJ   := $(patsubst %.cc,%.o,$(TEST_SRC))
-CXX        ?= g++
-CXXSTD     ?= $(shell $(CXX) -std=c++17 -c test/test.cc -o /dev/null 2>/dev/null && echo -std=c++17 || echo -std=c++11)
-CXXFLAGS   := $(CXXSTD) $(filter-out -std=gnu11,$(CFLAGS))
 TAR        ?= $(shell which gnu-tar || echo tar)
 ZIP        ?= $(shell which zip || echo "echo 'Please install zip'")
 CLANG_FORMAT ?= $(shell (which clang-format-12 || which clang-format-11 || which clang-format-10 || which clang-format) 2>/dev/null)
diff --git a/mdbx.h++ b/mdbx.h++
index 1e1fec9b..50824fb9 100644
--- a/mdbx.h++
+++ b/mdbx.h++
@@ -33,7 +33,6 @@
 #include <cassert>     // for assert()
 #include <cstring>     // for std::strlen, str:memcmp
 #include <exception>   // for std::exception_ptr
-#include <memory>      // for std::uniq_ptr
 #include <ostream>     // for std::ostream
 #include <sstream>     // for std::ostringstream
 #include <stdexcept>   // for std::invalid_argument
@@ -2220,7 +2219,7 @@ public:
   /// pages) in bytes.
   size_t size_current() const {
     assert(is_readwrite());
-    return get_info().txn_space_dirty;
+    return size_t(get_info().txn_space_dirty);
   }
 
   //----------------------------------------------------------------------------
diff --git a/src/internals.h b/src/internals.h
index f05b7f45..c4dfeec7 100644
--- a/src/internals.h
+++ b/src/internals.h
@@ -422,7 +422,7 @@ typedef sem_t mdbx_ipclock_t;
 #error "FIXME"
 #endif /* MDBX_LOCKING */
 
-#if MDBX_LOCKING > MDBX_LOCKING_SYSV
+#if MDBX_LOCKING > MDBX_LOCKING_SYSV && !defined(__cplusplus)
 MDBX_INTERNAL_FUNC int mdbx_ipclock_stub(mdbx_ipclock_t *ipc);
 MDBX_INTERNAL_FUNC int mdbx_ipclock_destroy(mdbx_ipclock_t *ipc);
 #endif /* MDBX_LOCKING */
@@ -1027,6 +1027,7 @@ struct MDBX_env {
 #endif
 };
 
+#ifndef __cplusplus
 /*----------------------------------------------------------------------------*/
 /* Debug and Logging stuff */
 
@@ -1206,6 +1207,17 @@ MDBX_INTERNAL_FUNC void mdbx_rthc_global_init(void);
 MDBX_INTERNAL_FUNC void mdbx_rthc_global_dtor(void);
 MDBX_INTERNAL_FUNC void mdbx_rthc_thread_dtor(void *ptr);
 
+static __maybe_unused __inline void mdbx_jitter4testing(bool tiny) {
+#if MDBX_DEBUG
+  if (MDBX_DBG_JITTER & mdbx_runtime_flags)
+    mdbx_osal_jitter(tiny);
+#else
+  (void)tiny;
+#endif
+}
+
+#endif /* !__cplusplus */
+
 #define MDBX_IS_ERROR(rc)                                                      \
   ((rc) != MDBX_RESULT_TRUE && (rc) != MDBX_RESULT_FALSE)
 
@@ -1360,15 +1372,6 @@ pgno_sub(pgno_t base, pgno_t subtrahend) {
   return (subtrahend < base - MIN_PAGENO) ? base - subtrahend : MIN_PAGENO;
 }
 
-static __maybe_unused __inline void mdbx_jitter4testing(bool tiny) {
-#if MDBX_DEBUG
-  if (MDBX_DBG_JITTER & mdbx_runtime_flags)
-    mdbx_osal_jitter(tiny);
-#else
-  (void)tiny;
-#endif
-}
-
 __nothrow_const_function static __always_inline __maybe_unused bool
 is_powerof2(size_t x) {
   return (x & (x - 1)) == 0;
diff --git a/src/mdbx.c++ b/src/mdbx.c++
index 9303363f..a8924245 100644
--- a/src/mdbx.c++
+++ b/src/mdbx.c++
@@ -12,7 +12,7 @@
  * <http://www.OpenLDAP.org/license.html>. */
 
 //
-// Non-inline part of the libmdbx C++ API (preliminary draft)
+// Non-inline part of the libmdbx C++ API (preliminary)
 //
 
 #ifdef _MSC_VER
@@ -25,7 +25,7 @@
 #include "internals.h"
 
 #include <atomic>
-#include <cctype> // for isxdigit()
+#include <cctype> // for isxdigit(), etc
 #include <system_error>
 
 #if defined(__has_include) && __has_include(<version>)
diff --git a/src/osal.h b/src/osal.h
index cdfe8965..9c2e476b 100644
--- a/src/osal.h
+++ b/src/osal.h
@@ -409,6 +409,55 @@ typedef pthread_mutex_t mdbx_fastmutex_t;
 #endif
 #endif /* __BYTE_ORDER__ || __ORDER_LITTLE_ENDIAN__ || __ORDER_BIG_ENDIAN__ */
 
+/* Get the size of a memory page for the system.
+ * This is the basic size that the platform's memory manager uses, and is
+ * fundamental to the use of memory-mapped files. */
+__nothrow_const_function static __maybe_unused __inline size_t
+mdbx_syspagesize(void) {
+#if defined(_WIN32) || defined(_WIN64)
+  SYSTEM_INFO si;
+  GetSystemInfo(&si);
+  return si.dwPageSize;
+#else
+  return sysconf(_SC_PAGE_SIZE);
+#endif
+}
+
+typedef struct mdbx_mmap_param {
+  union {
+    void *address;
+    uint8_t *dxb;
+    struct MDBX_lockinfo *lck;
+  };
+  mdbx_filehandle_t fd;
+  size_t limit;   /* mapping length, but NOT a size of file nor DB */
+  size_t current; /* mapped region size, i.e. the size of file and DB */
+#if defined(_WIN32) || defined(_WIN64)
+  uint64_t filesize /* in-process cache of a file size. */;
+#endif
+#ifdef MDBX_OSAL_SECTION
+  MDBX_OSAL_SECTION section;
+#endif
+} mdbx_mmap_t;
+
+typedef union bin128 {
+  __anonymous_struct_extension__ struct { uint64_t x, y; };
+  __anonymous_struct_extension__ struct { uint32_t a, b, c, d; };
+} bin128_t;
+
+#if defined(_WIN32) || defined(_WIN64)
+typedef union MDBX_srwlock {
+  struct {
+    long volatile readerCount;
+    long volatile writerCount;
+  };
+  RTL_SRWLOCK native;
+} MDBX_srwlock;
+#endif /* Windows */
+
+#ifdef __cplusplus
+extern void mdbx_osal_jitter(bool tiny);
+#else
 /*----------------------------------------------------------------------------*/
 /* Memory/Compiler barriers, cache coherence */
 
@@ -508,20 +557,6 @@ MDBX_INTERNAL_VAR bool
     mdbx_RunningOnWSL /* Windows Subsystem for Linux is mad and trouble-full */;
 #endif /* Linux */
 
-/* Get the size of a memory page for the system.
- * This is the basic size that the platform's memory manager uses, and is
- * fundamental to the use of memory-mapped files. */
-__nothrow_const_function static __maybe_unused __inline size_t
-mdbx_syspagesize(void) {
-#if defined(_WIN32) || defined(_WIN64)
-  SYSTEM_INFO si;
-  GetSystemInfo(&si);
-  return si.dwPageSize;
-#else
-  return sysconf(_SC_PAGE_SIZE);
-#endif
-}
-
 #ifndef mdbx_strdup
 LIBMDBX_API char *mdbx_strdup(const char *str);
 #endif
@@ -601,23 +636,6 @@ MDBX_INTERNAL_FUNC int mdbx_closefile(mdbx_filehandle_t fd);
 MDBX_INTERNAL_FUNC int mdbx_removefile(const char *pathname);
 MDBX_INTERNAL_FUNC int mdbx_is_pipe(mdbx_filehandle_t fd);
 
-typedef struct mdbx_mmap_param {
-  union {
-    void *address;
-    uint8_t *dxb;
-    struct MDBX_lockinfo *lck;
-  };
-  mdbx_filehandle_t fd;
-  size_t limit;   /* mapping length, but NOT a size of file nor DB */
-  size_t current; /* mapped region size, i.e. the size of file and DB */
-#if defined(_WIN32) || defined(_WIN64)
-  uint64_t filesize /* in-process cache of a file size. */;
-#endif
-#ifdef MDBX_OSAL_SECTION
-  MDBX_OSAL_SECTION section;
-#endif
-} mdbx_mmap_t;
-
 #define MMAP_OPTION_TRUNCATE 1
 #define MMAP_OPTION_SEMAPHORE 2
 MDBX_INTERNAL_FUNC int mdbx_mmap(const int flags, mdbx_mmap_t *map,
@@ -668,11 +686,6 @@ MDBX_INTERNAL_FUNC uint64_t
 mdbx_osal_16dot16_to_monotime(uint32_t seconds_16dot16);
 MDBX_INTERNAL_FUNC uint32_t mdbx_osal_monotime_to_16dot16(uint64_t monotime);
 
-typedef union bin128 {
-  __anonymous_struct_extension__ struct { uint64_t x, y; };
-  __anonymous_struct_extension__ struct { uint32_t a, b, c, d; };
-} bin128_t;
-
 MDBX_INTERNAL_FUNC bin128_t mdbx_osal_bootid(void);
 /*----------------------------------------------------------------------------*/
 /* lck stuff */
@@ -782,14 +795,6 @@ MDBX_INTERNAL_FUNC int mdbx_rpid_check(MDBX_env *env, uint32_t pid);
 
 #if defined(_WIN32) || defined(_WIN64)
 
-typedef union MDBX_srwlock {
-  struct {
-    long volatile readerCount;
-    long volatile writerCount;
-  };
-  RTL_SRWLOCK native;
-} MDBX_srwlock;
-
 typedef void(WINAPI *MDBX_srwlock_function)(MDBX_srwlock *);
 MDBX_INTERNAL_VAR MDBX_srwlock_function mdbx_srwlock_Init,
     mdbx_srwlock_AcquireShared, mdbx_srwlock_ReleaseShared,
@@ -909,6 +914,8 @@ static __inline bool mdbx_RunningUnderWine(void) {
 #error FIXME atomic-ops
 #endif
 
+#endif /* !__cplusplus */
+
 /*----------------------------------------------------------------------------*/
 
 #if defined(_MSC_VER) && _MSC_VER >= 1900