qt pro 里面变量的引用

• VAR = foobar => Assign value to variable when qmake is run
• $$VAR => QMake variable's value at the time qmake is run
• $${VAR} => QMake variable's value at the time qmake is run (identical but enclosed to separate from surrounding text)
• $(VAR) => Contents of an Environment variable at the time Makefile (not qmake) is run
• $$(VAR) =>Contents of an Environment variable at the time qmake (not Makefile) is run