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[bug #56206] ifndef false positive for exported variable
From: |
Paul D. Smith |
Subject: |
[bug #56206] ifndef false positive for exported variable |
Date: |
Sun, 12 May 2019 18:43:43 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0 |
Follow-up Comment #2, bug #56206 (project make):
Somehow my previous comment was truncated (I do so HATE Savannah markup :( ):
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
endif
Note that a variable set to an empty value is still defined, so ‘?=’ will
not set that variable.
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