remove old-style (C-style) casts (#1614)

Remove old-style (C-style) casts

This is required by the Google C++ style guide:
https://google.github.io/styleguide/cppguide.html#Casting

BUILD.bazel

@@ -49,6 +49,10 @@ cc_library(
         ":windows": ["-DEFAULTLIB:shlwapi.lib"],
         "//conditions:default": ["-pthread"],
     }),
+    copts = select({
+        ":windows": [],
+        "//conditions:default": ["-Werror=old-style-cast"],
+    }),
     strip_include_prefix = "include",
     visibility = ["//visibility:public"],
     # Only static linking is allowed; no .so will be produced.

CMakeLists.txt

@@ -175,6 +175,7 @@ else()
   add_cxx_compiler_flag(-Wextra)
   add_cxx_compiler_flag(-Wshadow)
   add_cxx_compiler_flag(-Wfloat-equal)
+  add_cxx_compiler_flag(-Wold-style-cast)
   if(BENCHMARK_ENABLE_WERROR)
       add_cxx_compiler_flag(-Werror)
   endif()

src/benchmark.cc

@@ -229,7 +229,7 @@ void State::PauseTiming() {
     for (const auto& name_and_measurement : measurements) {
       auto name = name_and_measurement.first;
       auto measurement = name_and_measurement.second;
-      BM_CHECK_EQ(std::fpclassify((double)counters[name]), FP_ZERO);
+      BM_CHECK_EQ(std::fpclassify(double{counters[name]}), FP_ZERO);
       counters[name] = Counter(measurement, Counter::kAvgIterations);
     }
   }

src/log.h

@@ -61,7 +61,7 @@ inline int& LogLevel() {
 }
 
 inline LogType& GetNullLogInstance() {
-  static LogType null_log((std::ostream*)nullptr);
+  static LogType null_log(static_cast<std::ostream*>(nullptr));
   return null_log;
 }