Cmake DEFINIERT tut scheint nicht zu erkennen Variable

Question

ich diesen Code in Cmake haben:

#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}) 

Das env var BOOST_HOME definiert ist (/ home/Ferran/Boost). Das Verhalten ist sehr seltsam, weil der Ausgang ist:

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


-- Configuring incomplete, errors occurred! 

Also, die var existiert und druckt dessen Inhalt und zugleich nicht existiert?

Answer 1

Sie benötigen dereferencing die Variable BOOST_DIR in der if Anweisung zu vermeiden:

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() 

von dereferencing BOOST_DIR, sind Sie effektiv die Abfrage, ob CMake eine Variable namens /home/ferran/boost definiert hat.