Modifying CACHE variable in CMake is not working

Question

I am using CMake 3.10.2 in Windows.

When I set the variable using CACHE like this

SET(ABAQUS_MAJORVERSION 2016)
SET(ABAQUS_MAJORVERSION ${ABAQUS_MAJORVERSION} CACHE STRING "" )

When I change the ABAQUS_MAJORVERSION variable to 2014 in GUI, this change is not updated in CMake. It keeps generating for 2016 version.

Please help in this regard. Thanks in Advance

Edit1:

This is the project structure:

|CMakeLists.txt
|FindABAQUS.cmake
|-project1
|---source1.cpp
|---CMakeLists.txt which has SET(ABAQUS_MAJORVERSION 2016 CACHE STRING "")  
|-project2
|---source2.cpp
|---CMakeLists.txt which has SET(ABAQUS_MAJORVERSION 2016 CACHE STRING "")

I changed the ABAQUS_MAJORVERSION to 2014 in GUI. The ABAQUS_MAJORVERSION became 2014 in CMakeCache.txt file. But when printed with message(${ABAQUS_MAJORVERSION }) it shows 2016

Solution:

example: SET(MAJORVERSION 2016 CACHE STRING "")

One might need to unset all the Include paths and library paths, to take effect of the new version Include path and library paths.

example: UNSET(INCLUDE_PATH CACHE)
         UNSET(LIBRARY_PATH CACHE)

I could not understand. Can you please explain in further detail or post a link relevant to this. Thanks — arun, Apr 16 '18 at 14:23
The linked Q&A does describe it in detail. Your first command sets a local variable `ABAQUS_MAJORVERSION`. You second command sets a cached variable `ABAQUS_MAJORVERSION`. The local variable supersedes the cached variable. If you just wanted to have a default merge both commands into `SET(ABAQUS_MAJORVERSION 2016 CACHE STRING "")`. — Florian, Apr 16 '18 at 14:36
@Florian: The referenced question and the answer doesn't describe such hiding. So it is hardly a duplicate. — Tsyvarev, Apr 16 '18 at 14:37
@Tsyvarev You're right. Sorry, have to add it there. But I'm pretty sure we covered that already in some other Q&A. Do you have a fitting duplicate? — Florian, Apr 16 '18 at 14:42
@Florian Thanks for the reply! I still face the same problem. I think I am missing something... I used `SET(ABAQUS_MAJORVERSION 2016 CACHE STRING "")` , but still could not change it in GUI — arun, Apr 16 '18 at 14:52
@Arun Just take a look into the `CMakeCache.txt` file in your binary output directory. If it says "2014" the change was successful. Then add a `variable_watch(ABAQUS_MAJORVERSION)` to your main `CMakeLists.txt` to see if some other code part is overwriting your setting. — Florian, Apr 16 '18 at 15:05
@Florian: That question - https://stackoverflow.com/questions/7294269/how-do-i-add-a-configuration-variable-to-my-cmake-script - looks more suitable as a duplicate. However, it is strange that it doesn't work for the question's author. @Arun: When you use [approach suggested by the Florian](https://stackoverflow.com/questions/49859504/modifying-cache-variable-in-cmake-is-not-working?noredirect=1#comment86734741_49859504), have you removed the first `set()` command? — Tsyvarev, Apr 16 '18 at 17:20
@Arun I have to admit I've never heard of an `EXTERNAL` cache variable type and I can't find a reference in [CMake's documentation](https://cmake.org/cmake/help/latest/command/set.html#set-cache-entry). Is this an undocumented feature and - if so - what exactly does it do? — Florian, May 06 '18 at 19:06
@Florian Apologize my misunderstanding. There is no EXTERNAL cache variable in CMake. The dereferencing variables by using UNSET(INCLUDE_PATH CACHE) only updated the newly entered CACHE variables. Without unset, I need to delete the CMakeCache.txt to update. I have corrected the error. — arun, May 07 '18 at 10:02
@arun You shouldn't edit your question in order to answer it. Instead, please [answer your own question!](https://stackoverflow.blog/2011/07/01/its-ok-to-ask-and-answer-your-own-questions/) — flaviut, May 21 '19 at 17:51

score 0 · Answer 1 · answered Aug 30 '22 at 05:47

It may depend on how you're using (or accidentally not using) the cache variable. You can have a normal variable and cache variable of the same name existing at the same time (which is exactly what you have going on) and still access them both (as per the docs on variable references) using ${var_name} for the regular variable, and $CACHE{var_name} for the cache variable.

This can trip people up because they aren't used to writing the explicit cache form, because usually the following behaviour takes effect:

When evaluating Variable References, CMake first searches the function call stack, if any, for a binding and then falls back to the binding in the current directory scope, if any. If a "set" binding is found, its value is used. If an "unset" binding is found, or no binding is found, CMake then searches for a cache entry. If a cache entry is found, its value is used. Otherwise, the variable reference evaluates to an empty string. The $CACHE{VAR} syntax can be used to do direct cache entry lookups.

I'm guessing this is what's tripping you up.

The following scenario can be another cause of confusion for anyone not aware of its behaviour, but I don't think it's what's tripping you up here.

In the CMake docs for setting cache variables:

Since cache entries are meant to provide user-settable values this does not overwrite existing cache entries by default. Use the FORCE option to overwrite existing entries.

For example, cache variables can be set on the command line with -D var_name:TYPE=VALUE.

Modifying CACHE variable in CMake is not working

1 Answers1