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Undefined symbols FlagRegister - cmake - fail to link gflags - Boost conflict #291

tgy opened this issue Oct 7, 2019 · 2 comments


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commented Oct 7, 2019

I have a problem in one of my projects where the program fails to compile because a linking error is raised on some gflags templated functions:

[100%] Linking CXX executable reproduce-issue
Undefined symbols for architecture x86_64:
  "google::FlagRegisterer::FlagRegisterer<bool>(char const*, char const*, char const*, b
ool*, bool*)", referenced from:
      ___cxx_global_var_init.3 in reproduce.cpp.o
  "google::FlagRegisterer::FlagRegisterer<int>(char const*, char const*, char const*, in
t*, int*)", referenced from:
      ___cxx_global_var_init in reproduce.cpp.o
ld: symbol(s) not found for architecture x86_64
clang-8: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [reproduce-issue] Error 1
make[2]: *** [CMakeFiles/reproduce-issue.dir/all] Error 2
make[1]: *** [CMakeFiles/reproduce-issue.dir/rule] Error 2
make: *** [reproduce-issue] Error 2

I have managed to reproduce this issue with a small example. Here are the CMakeLists.txt and reproduce.cpp files:

cmake_minimum_required(VERSION 3.6 FATAL_ERROR)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++1z -Wall -W -pedantic -g")
    "${CMAKE_CXX_FLAGS} -std=c++1z -Wall -W -pedantic -g")

project(reproduce LANGUAGES CXX)


find_package(Boost 1.62.0 REQUIRED)

target_link_libraries(reproduce-issue gflags)
#include <gflags/gflags.h>

DEFINE_int32(j, -1, "nb of jobs");
DEFINE_bool(skip, false, "whether to skip already done computations");

int main(void)
  return 0;

Note that the last version of gflags is cloned next to these two files.

Note also that if I move the add_subdirectory(gflags) instruction after include_directories(${Boost_INCLUDE_DIRS}) everything works fine.


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commented Oct 8, 2019

A few more details about which OS, compiler + version, and Boost library you are using may be needed. I tried your reproduce example on macOS 10.14.6 with clang 11.0.0 and Boost 1.70 (installed with Homebrew) and it compiled without any error.


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commented Oct 9, 2019

$ $CXX --version
clang version 8.0.1 (tags/RELEASE_801/final)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /usr/local/Cellar/llvm/8.0.1/bin
$ grep BOOST_LIB_VERSION `locate 'boost/version.hpp'`
//  BOOST_LIB_VERSION must be defined to be the same as BOOST_VERSION
#define BOOST_LIB_VERSION "1_70"
viovene@223-239 ~/p/phd/mdnotes (master)
$ sw_vers
ProductName:    Mac OS X
ProductVersion: 10.14.6
BuildVersion:   18G87
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