title: Why am I keeping get this error message? xxx.so undefined reference to `absl::StrCat[abi:cxx11](absl::AlphaNum const& ...)`
body: <p>I am keeping get those error messages when I do catkin_make in ROS, Ubuntu 16.04.</p>
  <p><code>xxx.so undefined reference to absl::StrCat[abi:cxx11](absl::AlphaNum const&amp; ...)</code></p>
  <p><code>xxx.so undefined reference to absl::String_internal::CatPieces[abi:cxx11]</code></p>
  <p><code>xxx.so undefined reference to absl::numbers_internal::FasIntToBuffer(int,char*)</code></p>
  <p><code>xxx.so undefined reference to absl::numbers_internal::SixDigitsToBuffer(double, char*)</code></p>
  <p>I git clone the abseil.cpp libary from github and <code>mkdir build</code> and <code>install</code> folder for build and install.
  Then <code>cp</code> the <code>install/include</code> to <code>usr/local/include</code>, I also pack all .a files to <code>libabsl.a</code> and <code>cp</code> to <code>usr/lib</code></p>
  <p>Here is my CMakeLists.txt file</p>
  <p><code>set(absl_INCLUDE_DIR &quot;/usr/local/include)</code></p>
  <p><code>set(absl_LIBS &quot;/usr/lib/libabsl.a)</code></p>
  <p><code>find_package(absl REQUIRED)</code></p>
  <p><code>include_directories(...${absl_INCLUDE_DIR})</code></p>
  <p><code>target_link_libraries(${PROJECT_NAME}_node   ${absl_LIBS}</code></p>
  <p>What might have caused those errors?</p>