An example of what will cause it: Ideally you’d call a function instead, but there is a recommended workaround:

E.g: fatal error: #####/#######.h: No such file or directory Your CMakeLists.txt has a REQUIRES section? This example is specific to the Espressif ESP-IDF, may be different for other SDKs If you don’t have a REQUIRES list in CMakeLists.txt that is declaring dependencies on certain special components, you don’t have to add basic components as REQUIRES […]

Using a local variable of the same name in another part of the application Declaring a variable like this: creates it as visible across all translation units. Even if you don’t use it as “extern int MyVariableName;” somewhere else, it’s still visible across all files. If you go and do the same thing again, create […]

Things to check Have you included the .h file where the variable or function is defined as “extern”? Is the .c file included in CMakeLists.txt?

GCC compiler flags that control unused warnings include: -Wunused-function-Wunused-label-Wunused-parameter-Wunused-value-Wunused-variable-Wunused (=all of the above) Disable for a single file or section of code