I am using CMake 3.8.2, GNU make 4.2.1 and GCC 6.4.0 for my C++14 project and I noticed a strange behavior when building. I am using CMake for an out-of-source build in a sub-folder called "build" where I run cmake .. followed by make.
CMake runs fine without any errors and make will build all source files like I expect until it is done compiling and starts linking them. It will then fail with an error
[ 83%] ...
[100%] Linking CXX executable myproject
/usr/bin/ld: some-source-file.cc.o: undefined reference to symbol '_ZNKSt7__cxx1118basic_stringstreamIcSt11char_traitsIcESaIcEE3strEv@@GLIBCXX_3.4.21'
Interestingly it doesn't show any compiler warnings up to this point and only shows the above mentioned linker error.
Now when I ignore the error and simply run cmake .. and then make again (just like I did before) I get all the compiler warnings that my code should produce and everything links perfectly fine, even though I didn't change any code or CMake-related files in the meantime.
I can reproduce this behavior by deleting all files in the build dir by running rm -r *.
Here is my CMakeLists.txt file:
# Define minimum required CMake version
cmake_minimum_required(VERSION 3.8.2)
# Setting compiler related settings
set(CMAKE_CXX_COMPILER "${CMAKE_SOURCE_DIR}/toolchain/binary/gcc-6.4.0/bin/gcc")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Wconversion -O2 -lstdc++")
set(CMAKE_CXX_STANDARD 14)
# Define project name
project(MyProject)
# Find source files
file(GLOB_RECURSE SOURCES application/*.cc)
# Adding third-party sources
set(SOURCES ${SOURCES} "third-party/cpp-base64/base64.cpp")
# Executable to be built from which source files
add_executable(myproject ${SOURCES})
# Find and include and link Botan
find_library(BOTAN botan-2 "third-party/botan/build/lib")
include_directories("third-party/botan/build/include/botan-2")
# Includes that are part of the project
include_directories("${CMAKE_SOURCE_DIR}/application/include")
# Include nlohmann/json
include_directories("third-party/json/src")
# Include cpp-base64 by René Nyffenegger
include_directories("third-party/cpp-base64")
find_package(Boost REQUIRED COMPONENTS program_options)
if(Boost_FOUND)
include_directories(${Boost_INCLUDE_DIRS})
endif()
# Link third-party libraries
target_link_libraries(myproject ${Boost_LIBRARIES} ${BOTAN})
Note: I am required to check-in the compiler and libraries I am using, which is why I specified them in the CMake file.
If it only works the second time it has to do with cached variables.
So I'm pretty sure that it will work the first time if you modify CMAKE_CXX_COMPILER setting by adding set(... CACHE INTERNAL "") to:
set(CMAKE_CXX_COMPILER "${CMAKE_SOURCE_DIR}/toolchain/binary/gcc-6.4.0/bin/gcc" CACHE INTERNAL "")
And move set(CMAKE_CXX_FLAGS ...) after the project() command.
But please also be noted that you shouldn't put the compiler into your CMakeLists.txt.
References
来源：https://stackoverflow.com/questions/47684410/cmake-and-make-need-to-be-run-twice-in-order-to-build-code-successfully