View Full Version : a question about makefile
August 20th, 2009, 04:30 AM
today I met a makefile having a line like:
TMP ?= /tmp
What does the "?" mean here.
August 20th, 2009, 05:03 AM
There is another assignment operator for variables, `?='. This is called a conditional variable assignment operator, because it only has an effect if the variable is not yet defined. This statement:
FOO ?= bar
is exactly equivalent to this (see The origin Function):
ifeq ($(origin FOO), undefined)
FOO = bar
August 22nd, 2009, 05:32 PM
thank you for providing the link, which is good.
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