[CMake] Why doesn't cmake generate the file?

[Michael Wild]

On 2. Dec, 2009, at 20:22 , Tyler Roscoe wrote:

> On Wed, Dec 02, 2009 at 07:58:43PM +0100, Jörg Förstner wrote:
>> I thought CMake would find the custom command and generate the file  
>> "gen.h"
>> Instead an error occurs, this is the output:
>>
>> -- Configuring done
>> CMake Error in libfoo.so/CMakeLists.txt:
>>  Cannot find source file "gen.h".  Tried extensions .c .C .c++ .cc
>>  .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp .hxx .in .txx
>>
>> Why doesn't CMake generate the file?
>
>> ------------------
>> # Set variable containing all source files
>> SET( SRCS
>>  foo1.c
>> )
>>
>> # Tell CMake that "gen.h" is a generated file
>> SET_SOURCE_FILE_PROPERTIES( gen.h PROPERTIES GENERATED 1 )
>>
>> # Define custom command to generate "gen.h"
>> ADD_CUSTOM_COMMAND(
>>  OUTPUT  gen.h
>>  COMMAND echo "this command would generate 'gen.h' from data.txt"
>>  DEPENDS data.txt
>> )
>>
>> # Define to build a target shared object library named "libfoo.so"  
>> from the source files "${SRCS}".
>> # The file "foo1.c" depends on the generated include file "gen.h"
>> ADD_LIBRARY( foo SHARED ${SRCS} gen.h )
>> ------------------
>
> Conceptually this looks correct.
>
> Have you tried this with a custom command that actually creates gen.h?
> The example you posted just echoes and doesn't generate anything.
>
> tyler


Also, you might want to use full paths to gen.h (by e.g. prefixing $ 
{CMAKE_CURRENT_BINARY_DIR}, or wherever your program outputs gen.h).

Further, you don't need to set the source file property GENERATED.  
CMake does that for you in the ADD_CUSTOM_COMMAND(OUTPUT $ 
{CMAKE_CURRENT_BINARY_DIR}/gen.h ...).


Michael