用cmake干净地构建代码，当添加为外部项目时失败 [英] code builds cleanly with cmake, fails when added as an external project

问题描述

问题摘要.

我有一个使用CMake构建的项目A，可以干净地编译.

I have a project A that I build using CMake, which compiles cleanly.

但是，当我使用CMake的ExternalProject_Add命令将A拖入另一个项目B时，当编译到A点时，编译就会失败.

However, when I pull A into another project B using CMake's ExternalProject_Add command, compilation fails when it reaches the point of building A.

我遇到的那种错误.

编译B会出现这样的错误

Compiling B gives errors like this one

warning: rvalue references are a C++11 extension [-Wc++11-extensions]

开始编译A时(再次由ExternalProject_Add引入).

when it starts compiling A (which again, is brought in by ExternalProject_Add).

请注意，在所有涉及的CMakeList.txt文件中都设置了-std=c++11.

Note that -std=c++11 is set in all involved CMakeList.txt files.

请注意，我也正在使用ExternalProject_Add拉google项目，但这不会引起任何问题.

Note that I am also pulling a google project using ExternalProject_Add, but it does not cause any problems.

所涉及的CMakeLists.txt文件中的一些细节.

以下摘录来自A的CMakeLists.txt:

The following excerpt is from A's CMakeLists.txt:

# Use the C++11 standard.
set (CC_FLAGS "-std=c++11")

# Figure out the warning flags to use.
CHECK_CXX_COMPILER_FLAG("-pedantic-errors" SUPPORTS_PEDANTIC_ERRORS)
CHECK_CXX_COMPILER_FLAG("-Wall" SUPPORTS_WALL)
CHECK_CXX_COMPILER_FLAG("-Wextra" SUPPORTS_WEXTRA)

if (SUPPORTS_PEDANTIC) 
  set (CC_FLAGS "${CC_FLAGS} -pedantic")
endif()

# [omitted]... similarly for the rest of the flags.

set (CMAKE_CXX_FLAGS_RELEASE "-O3 ${CC_FLAGS}")
set (CMAKE_CXX_FLAGS_DEBUG "-O0 -g ${CC_FLAGS}")

以下内容来自B的CMakeLists.txt.不同的部分在星号(*)之后.

The following is from B's CMakeLists.txt. The part that differs comes after the asterisks (*).

# Use the C++11 standard.
set (CC_FLAGS "-std=c++11")

# Figure out the warning flags to use.
CHECK_CXX_COMPILER_FLAG("-pedantic-errors" SUPPORTS_PEDANTIC_ERRORS)
CHECK_CXX_COMPILER_FLAG("-Wall" SUPPORTS_WALL)
CHECK_CXX_COMPILER_FLAG("-Wextra" SUPPORTS_WEXTRA)

if (SUPPORTS_PEDANTIC) 
  set (CC_FLAGS "${CC_FLAGS} -pedantic")
endif()

# [omitted]... similarly for the rest of the flags.

set (CMAKE_CXX_FLAGS_RELEASE "-O3 ${CC_FLAGS}")
set (CMAKE_CXX_FLAGS_DEBUG "-O0 -g ${CC_FLAGS}")

# ************* DIFFERS HERE ************

ExternalProject_Add (
  projectA

  PREFIX "${projectA_prefix}"
  GIT_REPOSITORY "[omitted]"

  INSTALL_COMMAND ""
)

ExternalProject_Add (
   google_benchmark

   PREFIX "${GoogleBenchmarkPrefix}"
   GIT_REPOSITORY "https://github.com/google/benchmark.git"

   UPDATE_COMMAND ""

   BUILD_COMMAND make benchmark
   INSTALL_COMMAND ""
)

推荐答案

通过默认， CMAKE_BUILD_TYPE 为空，因此所有特定于配置的设置被忽略.

By default, CMAKE_BUILD_TYPE is empty, so all configuration-specific settings are omitted.

这就是为什么没有使用任何CMAKE_CXX_FLAGS_*变量的原因，因此该项目是在没有c++11的情况下构建的.

That is why none of your CMAKE_CXX_FLAGS_* variable is used, so the project is built without c++11.

例外是优化的关键字:

Exception is optimized keyword for target_link_libraries: it works as corresponded to any non-debug config.

优良作法是为项目提供默认的构建类型. 这篇文章建议很好用于此目的的模板:

Good practice is to provide default build type for the project. This post suggests nice template for that purpose:

# Set a default build type if none was specified
if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
  message(STATUS "Setting build type to 'Debug' as none was specified.")
  set(CMAKE_BUILD_TYPE Debug CACHE STRING "Choose the type of build." FORCE)
  # Set the possible values of build type for cmake-gui
  set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS "Debug" "Release"
    "MinSizeRel" "RelWithDebInfo")
endif()

这篇关于用cmake干净地构建代码，当添加为外部项目时失败的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！