cmake DEFINED似乎无法识别变量 [英] cmake DEFINED does not seems to recognize variable

问题描述

我在cmake中有以下代码：

I have this code in cmake:

#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})

定义了环境变量BOOST_HOME（/ home / ferran / boost）。行为很奇怪，因为输出为：

The env var BOOST_HOME is defined (/home/ferran/boost). The behavior is very odd because the output is:

-- 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存在并打印其内容，而同时不存在吗？

So, the var exists and prints its contents and at the same time does not exists?

推荐答案

您需要避免在 BOOST_DIR > if 语句：

You need to avoid dereferencing the variable BOOST_DIR in the if statement:

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()

通过取消引用 BOOST_DIR ，您可以有效地查询CMake是否具有名为的变量/ home / ferran / boost 定义。

By dereferencing BOOST_DIR, you're effectively querying if CMake has a variable called /home/ferran/boost defined.

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