[CMake] getting a build parameter from a file

[Dave Yost]

> On 2015-06-09, at 8:05 AM, David Cole <DLRdave at aol.com> wrote:
> 
> Why not just use configure_file

because I didn’t know about it. Thanks!

> 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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