[CMake] How to check/set CMAKE_INSTALL_PREFIX

[Brad King]

Eric Noulard wrote:
> What is the good way to change the default value of CMAKE_INSTALL_PREFIX
> besides the usual:

This question has come up several times and I've been deferring a fix
until a project-specified initial cache feature is implemented.  That
feature has been delayed because it is tricky.

I've just added a fix to CVS CMake for this.  It will be in 2.4.4 (the
upcoming patch release).  Basically your code needs to know whether the
current value of CMAKE_INSTALL_PREFIX was set by the user on the command
line or initialized by CMake.  Now when CMake initializes the variable
it also sets CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT to true.  This
enables projects to change the default install prefix like this:

IF(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
  SET(CMAKE_INSTALL_PREFIX
    "/opt/foo" CACHE PATH "FOO install prefix" FORCE
    )
ENDIF(CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)

-Brad