如何隐藏CMake变量?

我有一个CMake项目，该项目允许全局设置变量(在命令行上用 -DARDUINO_SDK_PATH =/a/b/c 设置)消失，即突然给定值不见了，导致致命错误.

I have a CMake project which lets a globally set variable (set with -DARDUINO_SDK_PATH=/a/b/c on command line) disappear i.e. suddenly the given value is gone which leads to a fatal error.

我知道有 种隐藏"变量的不同方法(例如，内部函数或外部项目)

I know there are different ways to "hide" a variable (e.g. inside functions or external projects)

就我而言:

• 未在代码中的任何地方中显式设置变量(例如，通过 set()或 find_path()))
• 导致错误的访问位于顶层(即不在函数内部)
• 有一些指令(即同一文件/行)，在一种情况下，变量具有的值是给定的，而下一次它消失了

• the variable is not being set explicitly anywhere in the code (e.g. via set() or find_path())
• the access which leads to the error is on top level (i.e. not inside a function)
• there are instructions (i.e. same file/line) where in one case the variable has the value it's been given and the next time it's gone

使用 variable_watch(ARDUINO_SDK_PATH)跟踪变量我可以看到在检查编译器之前一切正常:

Tracing the variable with variable_watch(ARDUINO_SDK_PATH) I can see that everything works fine before the compiler is being checked:

cmake -DARDUINO_SDK_PATH=/a/b/c <path>
...
... everything fine, ${DARDUINO_SDK_PATH} == '/a/b/c' everywhere
...

-- Check for working C compiler: /usr/bin/avr-gcc

...
... here the variable is empty and not being traced any more
...

这是我的建议:编译器检查(在终端上由检查工作的C编译器.. 所指示)是否具有自己的变量空间，并且不知道命令行中提供的变量?

Here is my suggestion: Does the compiler check (indicated by check for working C compiler .. on the terminal) have it's own variable space and does not know variables provided on command line?

注意:此问题是

Note: This question is a generalization of this question, which has become way too specialized but might offer some useful background information.