[CMake] getting a build parameter from a file

[David Cole]

Why not just use configure_file to write ${metals} into the file...
configure_file only actually touches/writes-to/updates the file if the
contents are different...

Then you can just depend on that file and you don't need a separate
timestamp file.


HTH,
David C.


On Tue, Jun 9, 2015 at 1:05 AM, Dave Yost <Dave at yost.com> wrote:
>
>
> First, my cmake code does this:
>
> sets ${metals} from a cmake command-line argument
> compares the contents of ${metals} against the contents of a file to note
> whether the variable is being changed since the last run of cmake
> writes the new value to that file for next time
> call an add_timestamp_file_target function. which touches the file
> metalsTimestamp if the variable is being changed or if the file doesn’t
> exist.
>
> Then comes this:
>
> set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DMETALS=\"\\\"${metals}\\\"\"")
> add_executable   (metals metals.cc)
> add_dependencies (metals metalsTimestamp)
>
>
> My add_timestamp_file_target function has to use one of
>    add_custom_target
>    add_custom_command
> to make metalsTimestamp visible to the add_dependencies function.
>
> Problem is, it seems that those commands have to touch the file every time
> cmake runs, but I want to touch it only when necessary.
>
> Is there a way to make this work?
>
>
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