[CMake] avoid rebuilding targets depending on generated source files

[Michael Hertling]

On 03/03/2012 10:36 PM, Ajay Panyala wrote:
> Try "cmake -E copy_if_different ..."
> 
> cmake -E copy_if_different build/test1.c build/tests/test1.c
> 
> That would work when make is run atleast once.
> When running make for the 1st time test1.c was never
> copied to build/tests before. So I would be comparing a file with
> another non-existant file and that would result in an error halting
> the make process.

No, it wouldn't; check it out:

% touch a
% rm -f b
% ls b
ls: cannot access b: No such file or directory
% cmake -E copy_if_different a b
% ls b
b
% cksum a b
4294967295 0 a
4294967295 0 b

Regards,

Michael

> On Sat, Mar 3, 2012 at 1:20 PM, Hendrik Sattler <post at hendrik-sattler.de>wrote:
> 
>> Am Samstag, 3. März 2012, 21:41:49 schrieb Ajay Panyala:
>>> I have a custom target which runs a command to generate
>>> a C source file say test1.c
>>>
>>> ADD_CUSTOM_TARGET(TestGen ALL
>>> COMMAND genExec ${PROJECT_SOURCE_DIR}/Main.java
>>> DEPENDS ${PROJECT_SOURCE_DIR}/Main.java
>>> )
>>>
>>> And I have a custom command that moves the generated *test1.c *
>>> to a new directory inside the build directory.
>>>
>>> ADD_CUSTOM_COMMAND(
>>> TARGET TestGen
>>> POST_BUILD
>>> COMMAND mv
>>> ARGS ${PROJECT_BINARY_DIR}/test1.c ${PROJECT_BINARY_DIR}/tests/
>>> )
>>>
>>> Each time I run make, the custom target is run (since custom targets are
>>> always
>>> out-of-date). But I want to avoid moving the new test1.c generated each
>>> time if build/test1.c is the same as build/tests/test1.c since there are
>>> other targets
>>> like add_executable and add_library later in the CMakelists file that are
>>>  re-built
>>> each time since they depend on test1.c
>>
>> Try "cmake -E copy_if_different ..."
>>
>> HS