Fix google#444 - Use BENCHMARK_HAS_CXX11 over __cplusplus. (google#446)

* Fix google#444 - Use BENCHMARK_HAS_CXX11 over __cplusplus.

MSVC incorrectly defines __cplusplus to report C++03, despite the compiler
actually providing C++11 or greater. Therefore we have to detect C++11 differently
for MSVC. This patch uses `_MSVC_LANG` which has been defined since
Visual Studio 2015 Update 3; which should be sufficient for detecting C++11.

Secondly this patch changes over most usages of __cplusplus >= 201103L to
check BENCHMARK_HAS_CXX11 instead.

* remove redunant comment

Author: EricWF

README.md

@@ -185,7 +185,7 @@ BENCHMARK_TEMPLATE(BM_Sequential, WaitQueue<int>)->Range(1<<0, 1<<10);
 Three macros are provided for adding benchmark templates.
 
 ```c++
-#if __cplusplus >= 201103L // C++11 and greater.
+#ifdef BENCHMARK_HAS_CXX11
 #define BENCHMARK_TEMPLATE(func, ...) // Takes any number of parameters.
 #else // C++ < C++11
 #define BENCHMARK_TEMPLATE(func, arg1)

include/benchmark/benchmark.h

@@ -164,7 +164,8 @@ BENCHMARK(BM_test)->Unit(benchmark::kMillisecond);
 #define BENCHMARK_BENCHMARK_H_
 
 
-#if __cplusplus >= 201103L
+// The _MSVC_LANG check should detect Visual Studio 2015 Update 3 and newer.
+#if __cplusplus >= 201103L || (defined(_MSVC_LANG) && _MSVC_LANG >= 201103L)
 #define BENCHMARK_HAS_CXX11
 #endif
 
@@ -921,7 +922,7 @@ class Fixture : public internal::Benchmark {
 #define BENCHMARK_RANGE2(n, l1, h1, l2, h2) \
   BENCHMARK(n)->RangePair({{(l1), (h1)}, {(l2), (h2)}})
 
-#if __cplusplus >= 201103L
+#ifdef BENCHMARK_HAS_CXX11
 
 // Register a benchmark which invokes the function specified by `func`
 // with the additional arguments specified by `...`.
@@ -941,7 +942,7 @@ class Fixture : public internal::Benchmark {
               #func "/" #test_case_name,                 \
               [](::benchmark::State& st) { func(st, __VA_ARGS__); })))
 
-#endif  // __cplusplus >= 11
+#endif  // BENCHMARK_HAS_CXX11
 
 // This will register a benchmark for a templatized function.  For example:
 //
@@ -962,7 +963,7 @@ class Fixture : public internal::Benchmark {
           new ::benchmark::internal::FunctionBenchmark(#n "<" #a "," #b ">", \
                                                        n<a, b>)))
 
-#if __cplusplus >= 201103L
+#ifdef BENCHMARK_HAS_CXX11
 #define BENCHMARK_TEMPLATE(n, ...)                       \
   BENCHMARK_PRIVATE_DECLARE(n) =                         \
       (::benchmark::internal::RegisterBenchmarkInternal( \

test/benchmark_test.cc

@@ -109,7 +109,7 @@ BENCHMARK_TEMPLATE2(BM_Sequential, std::vector<int>, int)
     ->Range(1 << 0, 1 << 10);
 BENCHMARK_TEMPLATE(BM_Sequential, std::list<int>)->Range(1 << 0, 1 << 10);
 // Test the variadic version of BENCHMARK_TEMPLATE in C++11 and beyond.
-#if __cplusplus >= 201103L
+#ifdef BENCHMARK_HAS_CXX11
 BENCHMARK_TEMPLATE(BM_Sequential, std::vector<int>, int)->Arg(512);
 #endif
 
@@ -197,7 +197,7 @@ static void BM_ManualTiming(benchmark::State& state) {
 BENCHMARK(BM_ManualTiming)->Range(1, 1 << 14)->UseRealTime();
 BENCHMARK(BM_ManualTiming)->Range(1, 1 << 14)->UseManualTime();
 
-#if __cplusplus >= 201103L
+#ifdef BENCHMARK_HAS_CXX11
 
 template <class... Args>
 void BM_with_args(benchmark::State& state, Args&&...) {
@@ -213,7 +213,7 @@ void BM_non_template_args(benchmark::State& state, int, double) {
 }
 BENCHMARK_CAPTURE(BM_non_template_args, basic_test, 0, 0);
 
-#endif  // __cplusplus >= 201103L
+#endif  // BENCHMARK_HAS_CXX11
 
 static void BM_DenseThreadRanges(benchmark::State& st) {
   switch (st.range(0)) {

test/cxx03_test.cc

@@ -8,6 +8,10 @@
 #error C++11 or greater detected. Should be C++03.
 #endif
 
+#ifdef BENCHMARK_HAS_CXX11
+#error C++11 or greater detected by the library. BENCHMARK_HAS_CXX11 is defined.
+#endif
+
 void BM_empty(benchmark::State& state) {
   while (state.KeepRunning()) {
     volatile std::size_t x = state.iterations();