Improve C++ build system

Author: DraTeots

cpp/CMakeLists.txt

@@ -7,7 +7,7 @@
 #   RCDB_TEST_CONNECTION="sqlite:///<path-to>.sqlite" ./build/test_rcdb_cpp
 # Create the test database with:  rcdb -c sqlite:///<path-to>.sqlite db init --add-cpp-tests --confirm
 
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.10)
 project(rcdb_cpp)
 
 option(WITH_MYSQL  "Compile with MySQL support" OFF)
@@ -95,18 +95,26 @@ if(WITH_SQLITE)
     list(APPEND TEST_SOURCE_FILES tests/test_sqlite_unity.cpp)
 endif()
 
+# Read examples and tests build with either backend (SQLite is the default).
 add_executable(test_rcdb_cpp ${TEST_SOURCE_FILES})
 add_executable(examples_simple            examples/simple.cpp)
 add_executable(examples_trigger_params    examples/get_trigger_params.cpp)
 add_executable(examples_fadc_masks        examples/get_fadc_masks.cpp)
-add_executable(examples_write_conditions  examples/write_conditions.cpp)
-add_executable(examples_write_array_to_json examples/write_array_to_json.cpp)
-add_executable(examples_write_objects_to_json examples/write_objects_to_json.cpp)
 
 target_link_libraries(test_rcdb_cpp ${DB_REQIRED_LIBRARIES} dl pthread sqlite3)
 target_link_libraries(examples_trigger_params ${DB_REQIRED_LIBRARIES} dl pthread)
 target_link_libraries(examples_simple            ${DB_REQIRED_LIBRARIES} dl pthread)
 target_link_libraries(examples_fadc_masks ${DB_REQIRED_LIBRARIES} dl pthread)
-target_link_libraries(examples_write_conditions ${DB_REQIRED_LIBRARIES} dl pthread)
-target_link_libraries(examples_write_array_to_json ${DB_REQIRED_LIBRARIES} dl pthread)
-target_link_libraries(examples_write_objects_to_json ${DB_REQIRED_LIBRARIES} dl pthread)
+
+# Writing to RCDB from C++ goes through WritingConnection, which is MySQL-only
+# (the SQLite provider is read-only). So the write examples are built only when
+# MySQL support is enabled.
+if(WITH_MYSQL)
+    add_executable(examples_write_conditions  examples/write_conditions.cpp)
+    add_executable(examples_write_array_to_json examples/write_array_to_json.cpp)
+    add_executable(examples_write_objects_to_json examples/write_objects_to_json.cpp)
+
+    target_link_libraries(examples_write_conditions ${DB_REQIRED_LIBRARIES} dl pthread)
+    target_link_libraries(examples_write_array_to_json ${DB_REQIRED_LIBRARIES} dl pthread)
+    target_link_libraries(examples_write_objects_to_json ${DB_REQIRED_LIBRARIES} dl pthread)
+endif()

cpp/examples/write_objects_to_json.cpp

@@ -7,6 +7,7 @@
 #include <iostream>
 
 #include "RCDB/WritingConnection.h"
+#include "RCDB/StringUtils.h"
 #include <tao/json.hpp>
 
 using namespace tao;

docs/Cpp.md

@@ -146,6 +146,11 @@ targets (e.g. `examples_trigger_params`). There is no separate install step or c
      * Getting RCDB stored files contents
      * Working with config file parser
 * [get_fadc_masks.cpp](https://github.com/JeffersonLab/rcdb/blob/main/cpp/examples/get_fadc_masks.cpp) (target `examples_fadc_masks`) - Reading FADC masks
+
+Writing to RCDB from C++ goes through `WritingConnection`, which is **MySQL-only** (the
+SQLite provider is read-only). The following write examples are therefore built only when
+configured with `-DWITH_MYSQL=ON`:
+
 * [write_conditions.cpp](https://github.com/JeffersonLab/rcdb/blob/main/cpp/examples/write_conditions.cpp) (target `examples_write_conditions`) - Writing conditions to RCDB from C++. It includes:  
      * Using WritingConnection
      * Adding condition values of different types