Common C++ Build Use Cases

Here you will find some of the most common use cases for building C++ projects with Bazel. If you have not done so already, get started with building C++ projects with Bazel by completing the tutorial Introduction to Bazel: Build a C++ Project.

For information on cc_library and hdrs header files, see cc_library.

Including multiple files in a target

You can include multiple files in a single target with glob. For example:

cc_library(
    name = "build-all-the-files",
    srcs = glob(["*.cc"]),
    hdrs = glob(["*.h"]),
)

With this target, Bazel will build all the .cc and .h files it finds in the same directory as the BUILD file that contains this target (excluding subdirectories).

Using transitive includes

If a file includes a header, then any rule with that file as a source (that is, having that file in the srcs, hdrs, or textual_hdrs attribute) should depend on the included header's library rule. Conversely, only direct dependencies need to be specified as dependencies. For example, suppose sandwich.h includes bread.h and bread.h includes flour.h. sandwich.h doesn't include flour.h (who wants flour in their sandwich?), so the BUILD file would look like this:

cc_library(
    name = "sandwich",
    srcs = ["sandwich.cc"],
    hdrs = ["sandwich.h"],
    deps = [":bread"],
)

cc_library(
    name = "bread",
    srcs = ["bread.cc"],
    hdrs = ["bread.h"],
    deps = [":flour"],
)

cc_library(
    name = "flour",
    srcs = ["flour.cc"],
    hdrs = ["flour.h"],
)

Here, the sandwich library depends on the bread library, which depends on the flour library.

Adding include paths

Sometimes you cannot (or do not want to) root include paths at the workspace root. Existing libraries might already have an include directory that doesn't match its path in your workspace. For example, suppose you have the following directory structure:

└── my-project
    ├── legacy
    │   └── some_lib
    │       ├── BUILD
    │       ├── include
    │       │   └── some_lib.h
    │       └── some_lib.cc
    └── MODULE.bazel

Bazel will expect some_lib.h to be included as legacy/some_lib/include/some_lib.h, but suppose some_lib.cc includes "some_lib.h". To make that include path valid, legacy/some_lib/BUILD will need to specify that the some_lib/include directory is an include directory:

cc_library(
    name = "some_lib",
    srcs = ["some_lib.cc"],
    hdrs = ["include/some_lib.h"],
    copts = ["-Ilegacy/some_lib/include"],
)

This is especially useful for external dependencies, as their header files must otherwise be included with a / prefix.

Include external libraries

Suppose you are using Google Test {: .external}. You can add a dependency on it in the MODULE.bazel file to download Google Test and make it available in your repository:

bazel_dep(name = "googletest", version = "1.15.2")

Writing and running C++ tests

For example, you could create a test ./test/hello-test.cc, such as:

#include "gtest/gtest.h"
#include "main/hello-greet.h"

TEST(HelloTest, GetGreet) {
  EXPECT_EQ(get_greet("Bazel"), "Hello Bazel");
}

Then create ./test/BUILD file for your tests:

cc_test(
    name = "hello-test",
    srcs = ["hello-test.cc"],
    copts = [
      "-Iexternal/gtest/googletest/include",
      "-Iexternal/gtest/googletest",
    ],
    deps = [
        "@googletest//:gtest_main",
        "//main:hello-greet",
    ],
)

To make hello-greet visible to hello-test, you must add "//test:__pkg__", to the visibility attribute in ./main/BUILD.

Now you can use bazel test to run the test.

bazel test test:hello-test

This produces the following output:

INFO: Found 1 test target...
Target //test:hello-test up-to-date:
  bazel-bin/test/hello-test
INFO: Elapsed time: 4.497s, Critical Path: 2.53s
//test:hello-test PASSED in 0.3s

Executed 1 out of 1 tests: 1 test passes.

Adding dependencies on precompiled libraries

If you want to use a library of which you only have a compiled version (for example, headers and a .so file) wrap it in a cc_library rule:

cc_library(
    name = "mylib",
    srcs = ["mylib.so"],
    hdrs = ["mylib.h"],
)

This way, other C++ targets in your workspace can depend on this rule.