CMake install路径指定

在cmake项目里，最终生成的可执行文件往往需要一些配置才能正常运行，这些配置可能会存储入var, etc目录，不建议自己写死install路径，或者将install的函数再封装都是不推荐的，毕竟会增加额外的耦合，推荐用cmake内置变量指定安装文件，如下：

CMAKE_INSTALL_BINDIR: bin
CMAKE_INSTALL_DOCDIR: share/doc
CMAKE_INSTALL_INCLUDEDIR: include
CMAKE_INSTALL_DATADIR: share
CMAKE_INSTALL_INFODIR: share/info
CMAKE_INSTALL_LIBDIR: lib
CMAKE_INSTALL_MANDIR: share/man
CMAKE_INSTALL_SBINDIR: sbin
CMAKE_INSTALL_LIBEXECDIR: libexec
CMAKE_INSTALL_SYSCONFDIR: etc
CMAKE_INSTALL_SHAREDSTATEDIR: com
CMAKE_INSTALL_LOCALSTATEDIR: var
CMAKE_INSTALL_RUNSTATEDIR: var/run
CMAKE_INSTALL_DATAROOTDIR: share
CMAKE_INSTALL_LOCALEDIR: share/locale

install(TARGETS my_executable DESTINATION ${CMAKE_INSTALL_BINDIR})
install(FILES my_config.conf DESTINATION ${CMAKE_INSTALL_SYSCONFDIR})
install(FILES my_data_file DESTINATION ${CMAKE_INSTALL_LOCALSTATEDIR})
...

需要注意的是需要导入系统配置，上面的CMake变量才会有值：

if(WIN32)
    include(InstallRequiredSystemLibraries)
elseif(UINIX)
    include(GNUInstallDirs)
endif()

详细参考如下：
GNUInstallDirs
InstallRequiredSystemLibraries

如果设置的CMAKE_INSTALL_PREFIX为/home/test/Download/install，那么文件会分别安装到：

/home/test/Download/install/bin
/home/test/Download/install/var
/home/test/Download/install/etc
...

如果重新设置以下路径为opt:

set(CMAKE_INSTALL_BINDIR "opt")
set(CMAKE_INSTALL_LOCALSTATEDIR "opt")
set(CMAKE_INSTALL_SYSCONFDIR "opt")

那么文件会分别安装到:

/home/test/Download/install/opt
/home/test/Download/install/opt
/home/test/Download/install/opt
...