On 2013-02-14 16:44, Shaun Williams wrote:
I learned something very valuable today about cmake after getting an
unexpected result with STREQUAL:
set(foo bar)
...
set(baz foo)
...
if("${baz}" STREQUAL "bar") # This evaluates to true.
...
I expected it to be false, because I was trying to get baz's value ("foo")
to compare with "bar". I thought that parameters explicitly quoted were
treated as strings.
Then I learned that the interpreter is the only one that sees quotes around
parameters, for the sole purpose of string interpolation and preventing
whitespace from splitting a parameter. Cmake commands do not see these
quotes. Therefore, STREQUAL can never know the difference between "baz" and
baz.
So, STREQUAL treats a parameter as a variable name if it is defined, but as
a string value if it is not. (I verified this in cmIfCommand.cxx)
Is this quote behavior well-known among cmake users? For others like me,
I'd like this behavior to be emphasized in the cmake docs for STREQUAL.
Yes, it is :-/.
This is why I take a page from autotools and try to always write:
if("x_${baz}" STREQUAL "x_bar")
(Or you can write 'if(baz STREQUAL'... er... well if your RHS for sure
cannot be a variable name - e.g. is empty, contains spaces, etc. - then
you can write your constructs assuming that auto-expansion will occur.
Personally, I'm going to stick with explicit expansion - guaranteeing an
empty value in case the variable is not set - and adding something to
make it unlikely that either side expands to a variable name to prevent
auto-expansion...)
--
Matthew
--
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