cmake DEFINED似乎不承认变量

Question

我在cmake中有这段代码：

#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!

那么，var是否存在并打印其内容并且同时不存在？

Answer 1

您需要避免在BOOST_DIR语句中取消引用变量if：

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是否定义了名为/home/ferran/boost的变量。