Hello, I am trying unsuccessfully to use directive compilers such as #ifdef #elif with Keil C v6.12 as follows: #if defined (TOTO) #include "toto.h" #elif defined (TATA) #include "tata.h" #elif defined (TITI) #include "titi.h" #endif I think it should work, but it doesn't. Before I was using : #if defined (TOTO) #include "toto.h" #endif #if defined (TATA) #include "tata.h" #endif #if defined (TITI) #include "titi.h" #endif But in some cases in my code that is not possible to do so, I have to use a #elif. If someone has experienced the same problem.... Thank you for your help Best regards, Christophe