Add benchmark_main target. (#601)

* Add benchmark_main library with support for Bazel.

* fix newline at end of file

* Add CMake support for benchmark_main.

* Mention optionally using benchmark_main in README.

BUILD.bazel

@@ -10,10 +10,13 @@ config_setting(
 
 cc_library(
     name = "benchmark",
-    srcs = glob([
-        "src/*.cc",
-        "src/*.h",
-    ]),
+    srcs = glob(
+        [
+            "src/*.cc",
+            "src/*.h",
+        ],
+        exclude = ["src/benchmark_main.cc"],
+    ),
     hdrs = ["include/benchmark/benchmark.h"],
     linkopts = select({
         ":windows": ["-DEFAULTLIB:shlwapi.lib"],
@@ -23,6 +26,15 @@ cc_library(
     visibility = ["//visibility:public"],
 )
 
+cc_library(
+    name = "benchmark_main",
+    srcs = ["src/benchmark_main.cc"],
+    hdrs = ["include/benchmark/benchmark.h"],
+    strip_include_prefix = "include",
+    visibility = ["//visibility:public"],
+    deps = [":benchmark"],
+)
+
 cc_library(
     name = "benchmark_internal_headers",
     hdrs = glob(["src/*.h"]),

README.md

@@ -118,7 +118,10 @@ BENCHMARK(BM_StringCopy);
 BENCHMARK_MAIN();
 ```
 
-Don't forget to inform your linker to add benchmark library e.g. through `-lbenchmark` compilation flag.
+Don't forget to inform your linker to add benchmark library e.g. through 
+`-lbenchmark` compilation flag. Alternatively, you may leave out the 
+`BENCHMARK_MAIN();` at the end of the source file and link against 
+`-lbenchmark_main` to get the same default behavior.
 
 The benchmark library will reporting the timing for the code within the `for(...)` loop.
 

src/CMakeLists.txt

@@ -11,6 +11,7 @@ file(GLOB
     *.cc
     ${PROJECT_SOURCE_DIR}/include/benchmark/*.h
     ${CMAKE_CURRENT_SOURCE_DIR}/*.h)
+list(FILTER SOURCE_FILES EXCLUDE REGEX "benchmark_main\\.cc")
 
 add_library(benchmark ${SOURCE_FILES})
 set_target_properties(benchmark PROPERTIES
@@ -39,6 +40,18 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "SunOS")
   target_link_libraries(benchmark kstat)
 endif()
 
+# Benchmark main library
+add_library(benchmark_main "benchmark_main.cc")
+set_target_properties(benchmark_main PROPERTIES
+  OUTPUT_NAME "benchmark_main"
+  VERSION ${GENERIC_LIB_VERSION}
+  SOVERSION ${GENERIC_LIB_SOVERSION}
+)
+target_include_directories(benchmark PUBLIC
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/../include>
+    )
+target_link_libraries(benchmark_main benchmark)
+
 set(include_install_dir "include")
 set(lib_install_dir "lib/")
 set(bin_install_dir "bin/")
@@ -65,7 +78,7 @@ configure_file("${PROJECT_SOURCE_DIR}/cmake/benchmark.pc.in" "${pkg_config}" @ON
 if (BENCHMARK_ENABLE_INSTALL)
   # Install target (will install the library to specified CMAKE_INSTALL_PREFIX variable)
   install(
-    TARGETS benchmark
+    TARGETS benchmark benchmark_main
     EXPORT ${targets_export_name}
     ARCHIVE DESTINATION ${lib_install_dir}
     LIBRARY DESTINATION ${lib_install_dir}

src/benchmark_main.cc

@@ -0,0 +1,17 @@
+// Copyright 2018 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "benchmark/benchmark.h"
+
+BENCHMARK_MAIN();

test/BUILD

@@ -53,5 +53,13 @@ cc_library(
   # FIXME: Add support for assembly tests to bazel.
   # See Issue #556
   # https://github.com/google/benchmark/issues/556
-  ) for test_src in glob(["*test.cc"], exclude = ["*_assembly_test.cc"])
+  ) for test_src in glob(["*test.cc"], exclude = ["*_assembly_test.cc", "link_main_test.cc"])
 ]
+
+cc_test(
+    name = "link_main_test",
+    size = "small",
+    srcs = ["link_main_test.cc"],
+    copts = TEST_COPTS,
+    deps = ["//:benchmark_main"],
+)

test/CMakeLists.txt

@@ -41,6 +41,10 @@ macro(compile_benchmark_test name)
   target_link_libraries(${name} benchmark ${CMAKE_THREAD_LIBS_INIT})
 endmacro(compile_benchmark_test)
 
+macro(compile_benchmark_test_with_main name)
+  add_executable(${name} "${name}.cc")
+  target_link_libraries(${name} benchmark_main)
+endmacro(compile_benchmark_test_with_main)
 
 macro(compile_output_test name)
   add_executable(${name} "${name}.cc" output_test.h)
@@ -109,6 +113,9 @@ add_test(map_test map_test --benchmark_min_time=0.01)
 compile_benchmark_test(multiple_ranges_test)
 add_test(multiple_ranges_test multiple_ranges_test --benchmark_min_time=0.01)
 
+compile_benchmark_test_with_main(link_main_test)
+add_test(link_main_test link_main_test --benchmark_min_time=0.01)
+
 compile_output_test(reporter_output_test)
 add_test(reporter_output_test reporter_output_test --benchmark_min_time=0.01)
 

test/link_main_test.cc

@@ -0,0 +1,8 @@
+#include "benchmark/benchmark.h"
+
+void BM_empty(benchmark::State& state) {
+  for (auto _ : state) {
+    benchmark::DoNotOptimize(state.iterations());
+  }
+}
+BENCHMARK(BM_empty);