Pass a variable at build time into externalNativeBuild in Android

Question

Is there a way to pass a constant at compile time into the externalNativeBuild gradle enclosure, and to be able to use it in code?

For example:

externalNativeBuild {
    cmake {
        arguments "-DTEST=" + rootProject.ext.value
    }
}

And the to be able to use it somehow like next:

void foo() {
   int bla = TEST;
   ....
}

Note that the above code is not working, as TEST is not recognized by the c++ compiler, which is what I am trying to solve.

Answer 1

The easiest solution will be to use add_definitions:

add_definitions(-DTEST=${TEST})

to your CMakeLists.txt file.

Another one would be to use configuration file

Basing on Native sample app from Android Studio:

1. Create file: config.h.in in the same folder as default native-lib.cpp with following contents:

   #ifndef NATIVEAPP1_CONFIG_H_IN
   #define NATIVEAPP1_CONFIG_H_IN
   
   #cmakedefine TEST ${TEST}
   
   #endif //NATIVEAPP1_CONFIG_H_IN
   

2. In CMakeLists.txt add:

   # This sets cmake variable to the one passed from gradle.
   # This TEST variable is available only in cmake but can be read in
   # config.h.in which is used by cmake to create config.h
   set(TEST ${TEST}) 
   
   configure_file( config.h.in ${CMAKE_BINARY_DIR}/generated/config.h )
   include_directories( ${CMAKE_BINARY_DIR}/generated/ ) 
   

(add it for example, above add_library call)

3. Finally, add #include "config.h" in you cod (ex. in native-lib.cpp) to use TEST macro.

4. Rebuild