[CMake] How to compile a file only when linking anyhow?

[Mark Jonas]

Hi Alex,

thanks for your input.

>  > How do I tell the custom command to run when the linker will be
>  > called? It should not run always because that would cause the linker
>  > to be called whenever I call make.

>  You could use something like:
>  ADD_CUSTOM_COMMAND(TARGET target POST_BUILD
>                    COMMAND touch build_timestamp.c)

I tried that before and it has a bad side effect: The linker is now
called every time I run make although the source did not change. What
I am shooting for is that build_timestamp.c is compiled only when the
application would be linked anyhow.

Additionally, the solution uses a command that wouldn't work if the
output of CMake would be e.g. a Visual Studio project.

>  then the file will be newer than the executable everytime the executable is
>  built (and have build_timestamp.c part of your regular set of source files).

Exactly. You might be asking now why I am insisting not calling the
linker when it is not really necessary. The reason is that the
application I would like to use CMake with has about 1,000,000 source
lines. Linking the little monster takes about 5 minutes on a modern
PC.

Do you have another idea?

TIA,
Mark