[CMake] CMake Error: Cannot determine link language for target "io".

[Hendrik Sattler]

Zitat von Mats Kindahl <mats at sun.com>:
> Hendrik Sattler wrote:
>> Zitat von Mats Kindahl <mats at Sun.COM>:
>>> I have an example case where I want to decide the subsystems to include
>>> dynamically. However, when running CMake, I get the error above.
>>>
>>> Anybody can tell me why I get the error and what to do about it?
>>
>> You could give your files a file ending like 'output.c' instead of just
>> 'output'. Or, if that is the normal file naming, set the LANGUAGE file
>> property and the LINKER_LANGUAGE target property.
>
> OK. Adding suffixes to the files did help, but IIRC, the manual said  
>  that CMake
> figures this out itself.

It does but it needs hints like file suffixes to do so. Either  
automatic with file ending or manually.

>> You have an additional problem: you use target 'io' before it is
>> defined. If the io library is not installed, yet, this will fail.
>
> Actually, in the first version (looking a little different, but   
> having the same dependency) made CMake resolve the dependency itself.
>
> Ideally, I would like to copy or build the libraries in a central "lib/"
> directory similar to how I copy all the include files to the "include/"
> directory, but how is that supported by CMake?

See
http://www.cmake.org/cmake/help/cmake2.6docs.html#variable:CMAKE_LIBRARY_OUTPUT_DIRECTORY

Or you use the INSTALL() directives to add the install target that you  
can use to install the files into a wanted directory structure.

> So, basically, each package can depend on a number of include files and
> libraries that have not yet been built, so somehow I need to specify  
>  rules for how to build it all in a good order.

Using target_link_libraries() already does this _if_ you defined the  
library with add_library() _before_ using target_link_libraries. You  
GLOB will apply alphabetic order. Don't use it if you need a specific  
order. Use an explicit list instead.

HS