CMake --help-policy CMP0020
CMake Warning (dev) in CMakeLists.txt: Policy CMP0020 is not set: Automatically link Qt executables to qtmain target on Windows. Run "cmake --help-policy CMP0020" for policy details. Use the cmake_policy command to set the policy and suppress this warning.This warning is for project developers. Use -Wno-dev to suppress it.
下面是CMake --help-policy CMP0020的解释
Automatically link Qt executables to qtmain target on Windows.
CMake 2.8.10 and lower required users of Qt to always specify a link dependency to the qtmain.lib static library manually on Windows. CMake 2.8.11 gained the ability to evaluate generator expressions while determining the link dependencies from IMPORTED targets. This allows CMake itself to automatically link executables which link to Qt to the qtmain.lib library when using IMPORTED Qt targets. For applications already linking to qtmain.lib, this should have little impact. For applications which supply their own alternative WinMain implementation and for applications which use the QAxServer library, this automatic linking will need to be disabled as per the documentation.
The OLD behavior for this policy is not to link executables to qtmain.lib automatically when they link to the QtCore IMPORTEDtarget. The NEW behavior for this policy is to link executables to qtmain.lib automatically when they link to QtCore IMPORTED target.
This policy was introduced in CMake version 2.8.11. CMake version 220.127.116.1131224-gdfbca warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.
use cmake_minimum_required(2.8.13) instead.