Remove using C++17 features in example.cc and tests.cc.

Author: Maxim Egorushkin

Makefile

@@ -151,7 +151,7 @@ cxxflags.gcc.debug := -Og -f{stack-protector-all,no-omit-frame-pointer} # -D_GLI
 cxxflags.gcc.release := -O3 -mtune=native -fno-{stack-protector,stack-clash-protection,move-loop-invariants} -falign-functions=64 -DNDEBUG ${cxxflags.gcc.asm.${ASM}}
 cxxflags.gcc.sanitize := ${cxxflags.gcc.debug} -fsanitize=thread
 cxxflags.gcc.sanitize2 := ${cxxflags.gcc.debug} -fsanitize=undefined,address
-cxxflags.gcc := -march=native -f{no-plt,no-math-errno,finite-math-only,message-length=0} -W{all,extra,error,no-maybe-uninitialized} ${cxxflags.gcc.${BUILD}}
+cxxflags.gcc := -march=native -f{no-plt,no-math-errno,finite-math-only,message-length=0} -W{all,extra,error,no-maybe-uninitialized,no-unused-variable} ${cxxflags.gcc.${BUILD}}
 ldflags.gcc.sanitize := ${ldflags.gcc.debug} -fsanitize=thread
 ldflags.gcc.sanitize2 := ${ldflags.gcc.debug} -fsanitize=undefined,address
 # ldflags.gcc := -fuse-ld=${use-ld.gcc} -Wl,--compress-debug-sections=zstd,-O2,--gc-sections ${ldflags.gcc.${BUILD}}
@@ -163,7 +163,7 @@ cxxflags.clang.debug := -O0 -fstack-protector-all $(and ${has_native},-march=nat
 cxxflags.clang.release := -O3 -fno-stack-protector -falign-functions=64 -DNDEBUG $(and ${has_native},-march=native -mtune=native)
 cxxflags.clang.sanitize := ${cxxflags.clang.debug} -fsanitize=thread
 cxxflags.clang.sanitize2 := ${cxxflags.clang.debug} -fsanitize=undefined,address
-cxxflags.clang := -stdlib=libstdc++ -f{no-plt,no-math-errno,finite-math-only,message-length=0} -W{all,extra,error} ${cxxflags.clang.${BUILD}}
+cxxflags.clang := -stdlib=libstdc++ -f{no-plt,no-math-errno,finite-math-only,message-length=0} -W{all,extra,error,no-unused-variable} ${cxxflags.clang.${BUILD}}
 ldflags.clang.debug := -latomic # A work-around for clang bug.
 ldflags.clang.sanitize := ${ldflags.clang.debug} -fsanitize=thread
 ldflags.clang.sanitize2 := ${ldflags.clang.debug} -fsanitize=undefined,address
@@ -208,7 +208,6 @@ endif
 exes := example tests benchmarks
 
 example_src := example.cc
-${build_dir}/example.o : cxxflags += -std=c++17 # example.cc uses c++17 features.
 
 tests_src := tests.cc
 ${build_dir}/tests.o : cppflags += -DBOOST_TEST_DYN_LINK=1

meson.build

@@ -13,21 +13,27 @@ threads_dep = dependency('threads')
 atomic_queue_dep = declare_dependency(include_directories : ['include'], dependencies : threads_dep)
 
 if get_option('tests')
+  cxx = meson.get_compiler('cpp')
+  wno_unused_variable = []
+  if cxx.get_id() == 'gcc' or cxx.get_id() == 'clang'
+    wno_unused_variable = ['-Wno-unused-variable']
+  endif
+
   unit_test_framework_dep = dependency('boost', modules : ['unit_test_framework'])
 
-  # Tests still compile with C++14, but benchmarks and example require C++17.
   tests_exe = executable(
     'tests',
     'src/tests.cc',
+    cpp_args : wno_unused_variable,
     dependencies : [atomic_queue_dep, unit_test_framework_dep],
   )
   test('tests', tests_exe)
 
   example_exe = executable(
     'example',
     'src/example.cc',
+    cpp_args : wno_unused_variable,
     dependencies : [atomic_queue_dep],
-    cpp_args: ['-std=c++17']
   )
   test('example', example_exe)
 endif
@@ -50,7 +56,7 @@ if get_option('benchmarks')
     ['src/benchmarks.cc', 'src/cpu_base_frequency.cc', 'src/huge_pages.cc'],
     include_directories : ['src'],
     dependencies : [atomic_queue_dep, dl_dep, xenium_dep, boost_dep, tbb_dep, moodycamel_dep],
-    cpp_args: ['-std=c++17']
+    override_options : ['cpp_std=c++17']
   )
   benchmark('benchmarks', benchmarks_exe)
 endif

src/example.cc

@@ -50,7 +50,7 @@ int main() {
         producer.join();
 
     // Tell consumers to terminate by pushing one 0 element for each consumer.
-    for([[maybe_unused]] auto& consumer : consumers)
+    for(auto& consumer : consumers)
         q.push(0);
     // Wait till consumers have terminated.
     for(auto& consumer : consumers)

src/tests.cc

@@ -79,7 +79,7 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(stress, Queue, stress_queues) {
 
     for(auto& t : producers)
         t.join();
-    for([[maybe_unused]] auto& consumer : consumers)
+    for(auto& consumer : consumers)
         q.push(STOP_MSG);
     for(auto& t : consumers)
         t.join();