Lazy Set
VARIABLE = value
Normal setting of a variable, but any other variables mentioned with the value
field are recursively expanded with their value at the point at which the variable is used, not the one it had when it was declared
Immediate Set
VARIABLE := value
Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.
Lazy Set If Absent
VARIABLE ?= value
Setting of a variable only if it doesn't have a value. value
is always evaluated when VARIABLE
is accessed. It is equivalent to
ifeq ($(origin VARIABLE), undefined)
VARIABLE = value
endif
See the documentation for more details.
Append
VARIABLE += value
Appending the supplied value to the existing value (or setting to that value if the variable didn't exist)
By default, Makefile targets are "file targets" - they are used to build files from other files. Make assumes its target is a file, and this makes writing Makefiles relatively easy:
foo: bar
create_one_from_the_other foo bar
However, sometimes you want your Makefile to run commands that do not represent physical files in the file system. Good examples for this are the common targets "clean" and "all". Chances are this isn't the case, but you may potentially have a file named clean
in your main directory. In such a case Make will be confused because by default the clean
target would be associated with this file and Make will only run it when the file doesn't appear to be up-to-date with regards to its dependencies.
These special targets are called phony and you can explicitly tell Make they're not associated with files, e.g.:
.PHONY: clean
clean:
rm -rf *.o
Now make clean
will run as expected even if you do have a file named clean
.
In terms of Make, a phony target is simply a target that is always out-of-date, so whenever you ask make <phony_target>
, it will run, independent from the state of the file system. Some common make
targets that are often phony are: all
, install
, clean
, distclean
, TAGS
, info
, check
.
Best Answer
I gues that you're using Mac OS X
qmake -spec macx-g++ x.pro
on Mac OS X to generate Makefileqmake x.pro
on linux to generate Makefile (default behaviour)qmake -spec win32-g++ x.pro
on Windows to generate Makefile