问题
i guess i'm missing something very obvious here, but it seems to me that the cmake variables CMAKE_FIND_LIBRARY_PREFIXES/CMAKE_FIND_LIBRARY_SUFFIXES are not set to any "decent" default value depending on the current system/settings! i've checked the cmake docs and google, but there seems nothing about it really.
for example, a simple CMakeLists.txt essentially calling find_package(OpenSSL REQUIRED) will break unless you set the variables in your main file or directly invoke cmake -DCMAKE_FIND_LIBRARY_PREFIXES=lib -DCMAKE_FIND_LIBRARY_SUFFIXES=.so .. (on ubuntu w openssl/libssl-dev installed)
on the other hand, the default values PREFIX/SUFFIX for targets are initialized "correctly" for each platform, even considering BUILD_SHARED_LIBS etc. why not for find_library?
does anyone know why/what the suggested (users) behaviour should be?
回答1:
cmake variables CMAKE_FIND_LIBRARY_PREFIXES/CMAKE_FIND_LIBRARY_SUFFIXES are not set to any "decent" default value
Why do you think so? For instance:
cmake_minimum_required(VERSION 3.1)
project(Foo)
message("prefix: ${CMAKE_FIND_LIBRARY_PREFIXES}")
message("suffix: ${CMAKE_FIND_LIBRARY_SUFFIXES}")
Linux (Ubuntu):
prefix: lib
suffix: .so;.a
Mac:
prefix: lib
suffix: .dylib;.so;.a
Windows (Visual Studio):
prefix:
suffix: .lib
calling find_package(OpenSSL REQUIRED) will break unless you set the variables in your main file
Just tested, works fine for me. Ubuntu 14.04. CMake 2.8.12.2 and CMake 3.1.0-rc2.
回答2:
so i'll answer this question myself again as i need more space than the comment allows.
The "something obvious" i've missed is that i accessed those values before invocation of "project(Foo)", and at that stage CMAKE_FIND_LIBRARY_PREFIXES and CMAKE_FIND_LIBRARY_SUFFIXES are not initialized yet.
good to know in any case!
I was checking conditions on whether the main project could be built at all, and that involved checking if the cmake version is new enough and should be downloaded&built before anything further. on the other side, by cmake convention, you need to specify which minimum version you need before you issue any project commands. you see the deadlock there? so if i needed to build a newer cmake version on-the-fly, OpenSSL should be included if possible. this was detected using find_package(OpenSSL), but that in turn accessed the un-initialized CMAKE_FIND_LIBRARY_PREFIXES and everything broke.
来源：https://stackoverflow.com/questions/28194215/default-values-for-cmake-find-library-prefixes-cmake-find-library-suffixes