add cmake option XLNT_CXX_LANG to set the targetted cxx standard

- valid options are 11, 14, and 17
- default is 14
- cmake will error if an invalid value is provided
- requires cmake >= 3.10.* to take effect in visual studio

.travis.yml

@@ -12,25 +12,6 @@ notifications:
 # set up build matrix
 matrix:
   include:
-    # ============= CODE COVERAGE ===============
-    # gcc-6, c++11, debug build, static linking, code coverage enabled
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-          sources:
-            - ubuntu-toolchain-r-test
-          packages:
-            - g++-6
-            - lcov
-      env:
-        - CXX_COMPILER=g++-6
-        - C_COMPILER=gcc-6
-        - BUILD_TYPE=Debug
-        - COVERAGE=ON
-        - STATIC=ON
-        - SAMPLES=OFF
-    
     # ============= GCC ==================
     # gcc-6, c++11, debug build, dynamic linking
     - os: linux
@@ -44,12 +25,13 @@ matrix:
       env:
         - CXX_COMPILER=g++-6
         - C_COMPILER=gcc-6
+        - CXX_VER=11
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=OFF
         - SAMPLES=OFF
         
-    # gcc-8, c++11, release build, static linking, samples + benchmarks compiled
+    # gcc-7, c++14, release build, static linking, samples + benchmarks compiled
     - os: linux
       compiler: gcc
       addons:
@@ -61,12 +43,13 @@ matrix:
       env:
         - CXX_COMPILER=g++-7
         - C_COMPILER=gcc-7
+        - CXX_VER=14
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=ON
         - SAMPLES=ON
         
-    # gcc-8, c++11, release build, static linking, samples + benchmarks compiled
+    # gcc-8, c++17, release build, static linking, samples + benchmarks compiled
     - os: linux
       compiler: gcc
       addons:
@@ -78,6 +61,7 @@ matrix:
       env:
         - CXX_COMPILER=g++-8
         - C_COMPILER=gcc-8
+        - CXX_VER=17
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=ON
@@ -97,11 +81,13 @@ matrix:
       env:
         - CXX_COMPILER=clang++-4.0
         - C_COMPILER=clang-4.0
+        - CXX_VER=11
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=OFF
         - SAMPLES=OFF
-    # clang 5, c++11, release build, dynamic linking, samples + benchmarks compiled
+        
+    # clang 5, c++14, release build, dynamic linking, samples + benchmarks compiled
     - os: linux
       compiler: clang
       addons:
@@ -114,11 +100,13 @@ matrix:
       env:
         - CXX_COMPILER=clang++-5.0
         - C_COMPILER=clang-5.0
+        - CXX_VER=14
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=ON
         - SAMPLES=ON
-    # clang 6, c++11, release build, static linking, samples compiled
+        
+    # clang 6, c++17, release build, static linking, samples compiled
     - os: linux
       compiler: clang
       addons:
@@ -131,11 +119,32 @@ matrix:
       env:
         - CXX_COMPILER=clang++-6.0
         - C_COMPILER=clang-6.0
+        - CXX_VER=17
         - BUILD_TYPE=Release
         - COVERAGE=OFF
         - STATIC=ON
         - SAMPLES=ON
 
+    # ============= CODE COVERAGE ===============
+    # gcc-6, c++11, debug build, static linking, code coverage enabled
+    - os: linux
+      compiler: gcc
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-6
+            - lcov
+      env:
+        - CXX_COMPILER=g++-6
+        - C_COMPILER=gcc-6
+        - CXX_VER=11
+        - BUILD_TYPE=Debug
+        - COVERAGE=ON
+        - STATIC=ON
+        - SAMPLES=OFF
+        
 before_install:
   - export CC=${C_COMPILER}
   - export CXX=${CXX_COMPILER}
@@ -158,7 +167,7 @@ script:
     
   - mkdir build
   - cd build
-  - cmake -D STATIC=$STATIC -D BENCHMARKS=$BENCHMARKS -D SAMPLES=$SAMPLES -D COVERAGE=$COVERAGE -D CMAKE_BUILD_TYPE=$BUILD_TYPE ..
+  - cmake .. -DXLNT_CXX_LANG=${CXX_VER} -DSTATIC=$STATIC -DBENCHMARKS=$BENCHMARKS -DSAMPLES=$SAMPLES -DCOVERAGE=$COVERAGE -DCMAKE_BUILD_TYPE=$BUILD_TYPE
   - cmake --build . -- -j2
   - ./tests/xlnt.test
 

CMakeLists.txt

@@ -7,6 +7,18 @@ set(COMBINED_PROJECT TRUE)
 # Library type
 option(STATIC "Set to ON to build xlnt as a static library instead of a shared library" OFF)
 
+# c++ language standard to use
+set(XLNT_LANGS 11 14 17)
+set(XLNT_CXX_LANG "14" CACHE STRING "c++ language features to compile with")
+# enumerate allowed values for cmake gui
+set_property(CACHE XLNT_CXX_LANG PROPERTY STRINGS ${XLNT_LANGS})
+# validate value is in XLNT_LANGS
+list(FIND XLNT_LANGS ${XLNT_CXX_LANG} index)
+if(index EQUAL -1)
+    message(FATAL_ERROR "XLNT_CXX_LANG must be one of ${XLNT_LANGS}")
+endif()
+
+
 # Optional components
 option(TESTS "Set to OFF to skip building test executable (in ./tests)" ON)
 option(SAMPLES "Set to ON to build executable code samples (in ./samples)" OFF)

source/CMakeLists.txt

@@ -1,11 +1,7 @@
 cmake_minimum_required(VERSION 3.1)
 project(xlnt VERSION 1.2)
 
-# Require C99 and C++11 compilers
+set(CXX_EXTENSIONS OFF)
-set(CMAKE_C_STANDARD 99)
-set(CMAKE_C_STANDARD_REQUIRED ON)
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 # Project metadata
 set(PROJECT_VENDOR "Thomas Fussell")
@@ -156,6 +152,8 @@ else()
   target_compile_definitions(xlnt PUBLIC XLNT_STATIC=1)
 endif()
 
+target_compile_features(xlnt PUBLIC cxx_std_${XLNT_CXX_LANG})
+
 # Includes
 target_include_directories(xlnt PUBLIC ${XLNT_INCLUDE_DIR})
 target_include_directories(xlnt PRIVATE ${XLNT_SOURCE_DIR})
@@ -178,8 +176,7 @@ if(MSVC)
   set_source_files_properties(${CMAKE_CURRENT_SOURCE_DIR}/detail/cryptography/aes.cpp
     PROPERTIES
     COMPILE_FLAGS "/wd\"4996\"")
-endif()
+else()
-
   # Platform- and file-specific settings, Clang
   if(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
     set_source_files_properties(${CMAKE_CURRENT_SOURCE_DIR}/detail/serialization/miniz.cpp
@@ -196,6 +193,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
 	  PROPERTIES
 	  COMPILE_FLAGS "-Wno-strict-aliasing")
   endif()
+endif()
 
 # Group files into pseudo-folders in IDEs
 source_group(xlnt FILES ${ROOT_HEADERS})

tests/CMakeLists.txt

@@ -1,9 +1,7 @@
 cmake_minimum_required(VERSION 3.1)
 project(xlnt.test)
 
-# Require C++11 compiler
+set(CXX_EXTENSIONS OFF)
-set(CMAKE_CXX_STANDARD 11)
-set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if(NOT COMBINED_PROJECT)
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/../source ${CMAKE_CURRENT_BINARY_DIR}/source)
@@ -48,6 +46,7 @@ target_include_directories(xlnt.test
 
 set(XLNT_TEST_DATA_DIR ${CMAKE_CURRENT_SOURCE_DIR}/data)
 target_compile_definitions(xlnt.test PRIVATE XLNT_TEST_DATA_DIR=${XLNT_TEST_DATA_DIR})
+target_compile_features(xlnt.test PRIVATE cxx_std_${XLNT_CXX_LANG})
 
 if(MSVC)
   # bigobj because there are so many headers in one source file