From 76bac8da7112084b08bba86ddfa58774ee490a88 Mon Sep 17 00:00:00 2001
From: Shahram Najm <masn@ecmwf.int>
Date: Sat, 21 May 2022 14:37:23 +0100
Subject: [PATCH] ECC-1393: CMake: Add option to build ecCodes with C++

---
 CMakeLists.txt        | 13 +++++++++++++
 src/CMakeLists.txt    |  8 ++++++++
 tools/CMakeLists.txt  |  7 +++++++
 tools/grib_get_data.c |  4 ++--
 tools/grib_tools.h    |  8 ++++++++
 5 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d4c7df8b0..df0920c04 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -65,6 +65,13 @@ ecbuild_info("Operating system=${CMAKE_SYSTEM} (${EC_OS_BITS} bits)")
 ###############################################################################
 # some variables/options of this project
 
+ecbuild_add_option( FEATURE EXPERIMENTAL_BUILD_WITH_CXX
+    DESCRIPTION "Build ecCodes with a C++ compiler (Experimental)"
+    DEFAULT OFF )
+if( HAVE_EXPERIMENTAL_BUILD_WITH_CXX )
+    enable_language( CXX )
+endif()
+
 ecbuild_add_option( FEATURE PRODUCT_GRIB
     DESCRIPTION "Support for the product GRIB"
     DEFAULT ON )
@@ -515,3 +522,9 @@ ecbuild_info("   | bindings from PyPI with:             |")
 ecbuild_info("   |   $ pip3 install eccodes             |")
 ecbuild_info("   +--------------------------------------+")
 ecbuild_info("")
+
+if( HAVE_EXPERIMENTAL_BUILD_WITH_CXX )
+    ecbuild_warn("Please note:\n"
+                 "The option of building with C++ is currently experimental."
+                 "Do not use in operations.")
+endif()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 37a2d00bf..ea0a12b4a 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -427,6 +427,14 @@ if( HAVE_MEMFS )
     list(APPEND ECCODES_EXTRA_LIBRARIES eccodes_memfs)
 endif()
 
+if( HAVE_EXPERIMENTAL_BUILD_WITH_CXX )
+    foreach( _src ${eccodes_src_files} )
+        get_filename_component( _ext ${_src} EXT )
+        if( _ext STREQUAL ".c" )
+            set_source_files_properties( ${_src} PROPERTIES LANGUAGE CXX )
+        endif()
+    endforeach()
+endif()
 
 ecbuild_add_library( TARGET    eccodes
                      SOURCES   ${CMAKE_CURRENT_BINARY_DIR}/grib_api_version.c
diff --git a/tools/CMakeLists.txt b/tools/CMakeLists.txt
index 781e6f22a..edae7ab62 100644
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -18,6 +18,10 @@ if( EC_OS_NAME MATCHES "windows" )
   list( APPEND ecc_tools_sources wingetopt.c )
 endif()
 
+if( HAVE_EXPERIMENTAL_BUILD_WITH_CXX )
+    set_source_files_properties(${ecc_tools_sources} PROPERTIES LANGUAGE CXX)
+endif()
+
 # tools library
 ecbuild_add_library( TARGET    ecc_tools
                      TYPE      STATIC
@@ -48,6 +52,9 @@ list( APPEND ecc_tools_binaries_extra
 # Install generic tools
 foreach( tool ${ecc_tools_binaries} )
     # here we use the fact that each tool has only one C file that matches its name
+    if( HAVE_EXPERIMENTAL_BUILD_WITH_CXX )
+        set_source_files_properties(${tool}.c PROPERTIES LANGUAGE CXX)
+    endif()
     ecbuild_add_executable( TARGET     ${tool}
                             SOURCES    ${tool}.c
                             LIBS       ecc_tools )
diff --git a/tools/grib_get_data.c b/tools/grib_get_data.c
index 4d0e054a7..69f409649 100644
--- a/tools/grib_get_data.c
+++ b/tools/grib_get_data.c
@@ -84,7 +84,7 @@ int grib_tool_new_handle_action(grib_runtime_options* options, grib_handle* h)
     char* format_values     = NULL;
     char format_latlons[32] = {0,};
     char* default_format_values  = "%.10e";
-    char* default_format_latlons = "%9.3f%9.3f";
+    const char* default_format_latlons = "%9.3f%9.3f";
     int print_keys               = grib_options_on("p:");
     long numberOfPoints          = 0;
     long bitmapPresent           = 0;
@@ -305,7 +305,7 @@ static grib_values* get_key_values(grib_runtime_options* options, grib_handle* h
     int i                      = 0;
     int ret                    = 0;
     char value[MAX_STRING_LEN] = {0,};
-    char* notfound = "not found";
+    const char* notfound = "not found";
 
     for (i = 0; i < options->print_keys_count; i++) {
         size_t len = MAX_STRING_LEN;
diff --git a/tools/grib_tools.h b/tools/grib_tools.h
index d11c8d11a..1ea85e216 100644
--- a/tools/grib_tools.h
+++ b/tools/grib_tools.h
@@ -45,6 +45,10 @@
 #define MODE_TAF 5
 #define MODE_ANY 6
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 typedef union grib_typed_value
 {
     long* long_value;
@@ -208,4 +212,8 @@ int grib_tool_new_filename_action(grib_runtime_options* options, const char* fil
 int grib_no_handle_action(grib_runtime_options* options, int err);
 int exit_if_input_is_directory(const char* toolname, const char* filename);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* GRIB_TOOLS_H */