Most often the answer to the question is “no.” As both the About Abseil page and our contributing guidelines explain, Abseil contains a variety of core C++ library code that is widely used at Google. As such, Abseil‘s primary purpose is to be used as a dependency by Google’s open source C++ projects. While we do hope that Abseil is also useful to the C++ community at large, this added constraint also means that we are unlikely to accept a contribution of utility code that isn't already widely used by Google.
The short answer is that whatever mechanism you choose, you need to make sure that you set this option consistently at the global level for your entire project. If, for example, you want to set the C++ dialect to C++17, with Bazel as the build system and gcc or clang as the compiler, there are several ways to do this: * Pass --cxxopt=-std=c++17 on the command line (for example, bazel build --cxxopt=-std=c++17 ...) * Set the environment variable BAZEL_CXXOPTS (for example, BAZEL_CXXOPTS=-std=c++17) * Add build --cxxopt=-std=c++17 to your .bazelrc file
If you are using CMake as the build system, you'll need to add a line like set(CMAKE_CXX_STANDARD 17) to your top level CMakeLists.txt file. If you are developing a library designed to be used by other clients, you should instead leave CMAKE_CXX_STANDARD unset and configure the minimum C++ standard required by each of your library targets via target_compile_features. See the CMake build instructions for more information.
For a longer answer to this question and to understand why some other approaches don't work, see the answer to “What is ABI and why don't you recommend using a pre-compiled version of Abseil?”
For the purposes of this discussion, ABI refers to the compiled representation of code interfaces. This contrasts with API, which refers to the interfaces defined in the source code. Abseil has a strong promise of API compatibility, but does not make any promise of ABI compatibility. Let's take a look at what this means in practice.
You might be tempted to do something like this in a Bazel BUILD file:
# DON'T DO THIS!!!
cc_library(
name = "my_library",
srcs = ["my_library.cc"],
copts = ["-std=c++17"], # May create a mixed-mode compile!
deps = ["@com_google_absl//absl/strings"],
)
Applying -std=c++17 to an individual target in your BUILD file is going to compile that specific target in C++17 mode, but it isn't going to ensure the Abseil library is built in C++17 mode, since the Abseil library itself is a different build target. If your code includes an Abseil header, then your program may contain conflicting definitions of the same class/function/variable/enum, etc. As a rule, all compile options that affect the ABI of a program need to be applied to the entire build on a global basis.
C++ has something called the One Definition Rule (ODR). C++ doesn't allow multiple definitions of the same class/function/variable/enum, etc. ODR violations sometimes result in linker errors, but linkers do not always catch violations. Uncaught ODR violations can result in strange runtime behaviors or crashes that can be hard to debug.
If you build the Abseil library and your code using different compile options that affect ABI, there is a good chance you will run afoul of the One Definition Rule. Examples of GCC compile options that affect ABI include (but aren't limited to) language dialect (e.g. -std=), optimization level (e.g. -O2), code generation flags (e.g. -fexceptions), and preprocessor defines (e.g. -DNDEBUG).
If you use a pre-compiled version of Abseil, (for example, from your Linux distribution package manager or from something like vcpkg) you have to be very careful to ensure ABI compatibility across the components of your program. The only way you can be sure your program is going to be correct regarding ABI is to ensure you've used the exact same compile options as were used to build the pre-compiled library. This does not mean that Abseil cannot work as part of a Linux distribution since a knowledgeable binary packager will have ensured that all packages have been built with consistent compile options. This is one of the reasons we warn against - though do not outright reject - using Abseil as a pre-compiled library.
Another possible way that you might run afoul of ABI issues is if you accidentally include two versions of Abseil in your program. Multiple versions of Abseil can end up within the same binary if your program uses the Abseil library and another library also transitively depends on Abseil (resulting in what is sometimes called the diamond dependency problem). In cases such as this you must structure your build so that all libraries use the same version of Abseil. Abseil's strong promise of API compatibility between releases means the latest “HEAD” release of Abseil is almost certainly the right choice if you are doing as we recommend and building all of your code from source.
For these reasons we recommend you avoid pre-compiled code and build the Abseil library yourself in a consistent manner with the rest of your code.
From Abseil's point-of-view, “live at head” means that every Abseil source release (which happens on an almost daily basis) is either API compatible with the previous release, or comes with an automated tool that you can run over code to make it compatible. In practice, the need to use an automated tool is extremely rare. This means that upgrading from one source release to another should be a routine practice that can and should be performed often.
We recommend you update to the latest commit in the master branch of Abseil as often as possible. Not only will you pick up bug fixes more quickly, but if you have good automated testing, you will catch and be able to fix any Hyrum's Law dependency problems on an incremental basis instead of being overwhelmed by them and having difficulty isolating them if you wait longer between updates.
If you are using the Bazel build system with Bzlmod, you can use a git_override in your MODULE.bazel file to track the latest commit.
For example, to update to the latest commit, you would add (or update) the following snippet in your MODULE.bazel file:
bazel_dep(name = "abseil-cpp", version = "20260107.1") git_override( module_name = "abseil-cpp", remote = "https://github.com/abseil/abseil-cpp.git", # Replace the following line with the latest commit. commit = "6ec9964c325db0610a376b3cb81de073ea6ada90", )
You can commit the updated MODULE.bazel file to your source control every time you update, and if you have good automated testing, you might even consider automating this.
Abseil's hash function uses a random seed.
Many programmers believe incorrectly that this is a defense against hash flooding. While it does make a hash flooding attack more difficult, Abseil's hash function prioritizes speed over thorough mixing (and thus is not cryptographically secure), and the current seed implementation is also not cryptographically secure. If you are storing a large amount of attacker-controlled data, the most reliable defense against hash-flooding is to use a container that does not have O(n) worst-case behavior.
The real reason for hash randomization is to prevent Hyrum's Law dependencies on iteration order. This has allowed us to roll out steady improvements to the implementation without breaking users who may have otherwise written code that was dependent on ordering or other characteristics.
The current implementation uses a global seed, which, if linked incorrectly (e.g., static Abseil in multiple DSOs), can cause the ODR violations. If more than one seed is linked, different calls to the hash function may return different values, rendering hash elements inaccessible, causing crashes, or other arbitrarily bad behaviors.
We are often asked for a knob to disable hash randomization. The answer is a hard “no”, even under test or under a flag, because people will find a way to force it and allow their code or tests to depend on it. At Google-scale, the compute costs that are saved by preserving the ability to improve the implementation far outweigh the inconvenience of learning how to write code resilient to change.
LLVM Sanitizers are a suite of powerful, dynamic analysis tools that automatically detect various critical bugs during program execution. They work by instrumenting the compiled binary and linking a runtime library to intercept operations and report issues.
We receive many incorrect bug reports from users trying to use the sanitizers. The most common cause of these issues is ODR violations in the form of an instrumentation mismatch. This happens when users try to link libraries compiled with sanitizer instrumentation with uninstrumented libraries. It is important that all code in the application is built with the same sanitizer configuration.
The easiest way to do this is to use Bazel and pass the sanitizer options on the commandline, but it is important not to overlook the importance of avoiding precompiled system libraries, including the C++ standard library. For instance, MemorySanitizer requires an instrumented libc++.
Since most users are not going to build libc++ with Bazel, here is a MemorySanitizer recipe that currently works (and could easily be tweaked for ThreadSanitizer and friends):
# From the root of the LLVM source tree, configure libc++ to be instrumented with MSAN: cmake -G Ninja -S runtimes -B build_msan -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="${HOME}/llvm-msan" -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_USE_SANITIZER=MemoryWithOrigins -DLLVM_TARGETS_TO_BUILD="host" # Build and install it into ${HOME}/llvm-msan ninja -C build_msan install-cxx install-cxxabi install-unwind # Then build (or test) your code like this: bazel test --repo_env=CC=clang --repo_env=BAZEL_CXXOPTS=nostdinc++ --repo_env=BAZEL_LINKOPTS=-L${HOME}/llvm-msan/lib:-lc++:-lc++abi:-lgcc_s:-lm:-Wl,-rpath=${HOME}/llvm-msan/lib --repo_env=CPLUS_INCLUDE_PATH=${HOME}/llvm-msan/include/c++/v1 --copt=-fsanitize=memory --linkopt=-fsanitize=memory --linkopt=-fsanitize-link-c++-runtime ...
You should consider adding these options to a .bazelrc file to avoid retyping them.