cmake DEFINED似乎不承认变量

Question

我在cmake中有这个代码:

#mandatory
SET(BOOST_DIR "$ENV{BOOST_HOME}")
if (DEFINED ${BOOST_DIR})
    #global include directories
    include_directories(${BOOST_DIR})
else(DEFINED ${BOOST_DIR})
    message( STATUS "BOOST_HOME at ${BOOST_DIR}")

    message( FATAL_ERROR "Undefined BOOST_HOME env var.")
endif(DEFINED ${BOOST_DIR})

定义了env var BOOST_HOME(/ home/ferran/boost).行为很奇怪,因为输出是:

-- BOOST_HOME at /home/ferran/boost
CMake Error at CMakeLists.txt:14 (message):
  Undefined BOOST_HOME env var.


-- Configuring incomplete, errors occurred!

因此,var存在并打印其内容并且同时不存在？

Answer 1

您需要避免BOOST_DIR在if语句中取消引用该变量:

set(BOOST_DIR "$ENV{BOOST_HOME}")
if(BOOST_DIR)               # <--- Use 'BOOST_DIR', not 'DEFINED ${BOOST_DIR}'
    #global include directories
    include_directories(${BOOST_DIR})
else()
    message(STATUS "BOOST_HOME at ${BOOST_DIR}")
    message(FATAL_ERROR "Undefined BOOST_HOME env var.")
endif()

通过解除引用BOOST_DIR,您可以有效地查询CMake是否有一个名为/home/ferran/boostdefined 的变量.