Report unrecognized arguments from BENCHMARK_MAIN() macro (#332)

* BENCHMARK_MAIN() now reports unrecognised command-line flags (see google/benchmark#320)

* add benchmark::ReportUnrecognizedArguments()

Update BENCHMARK_MAIN() to use ReportUnrecognizedArguments() instead of
having the reporting code directly in the macro.

See issue google/benchmark#320 for reference

* let's stick to american english -- fix type in ReportUnrecognizedArguments()

* make ReportUnrecognizedArguments() print to stderr

* make ReportUnrecognizedArguments() return true if any arguments have been reported (i.e. argc > 1)

include/benchmark/benchmark_api.h

@@ -168,6 +168,10 @@ class BenchmarkReporter;
 
 void Initialize(int* argc, char** argv);
 
+// Report to stdout all arguments in 'argv' as unrecognized except the first.
+// Returns true there is at least on unrecognized argument (i.e. 'argc' > 1).
+bool ReportUnrecognizedArguments(int argc, char** argv);
+
 // Generate a list of benchmarks matching the specified --benchmark_filter flag
 // and if --benchmark_list_tests is specified return after printing the name
 // of each matching benchmark. Otherwise run each matching benchmark and
@@ -858,6 +862,7 @@ class Fixture : public internal::Benchmark {
 #define BENCHMARK_MAIN()                   \
   int main(int argc, char** argv) {        \
     ::benchmark::Initialize(&argc, argv);  \
+    if (::benchmark::ReportUnrecognizedArguments(argc, argv)) return 1; \
     ::benchmark::RunSpecifiedBenchmarks(); \
   }
 

src/benchmark.cc

@@ -664,4 +664,11 @@ void Initialize(int* argc, char** argv) {
   internal::LogLevel() = FLAGS_v;
 }
 
+bool ReportUnrecognizedArguments(int argc, char** argv) {
+  for (int i = 1; i < argc; ++i) {
+    fprintf(stderr, "%s: error: unrecognized command-line flag: %s\n", argv[0], argv[i]);
+  }
+  return argc > 1;
+}
+
 }  // end namespace benchmark