Preprocessor equality test, is this standard?

Question

I had envisaged one of these in the project preferences

• TESTING = HOST
• TESTING = TARGET

Answer 1

The original C preprocessors required explicit #ifdef validation before using a symbol. It is a relatively recent innovation (perhaps driven by scripting languages like Javascript) to assume that undefined symbols have a default value.

Why don't you always insure the symbol is defined?:

#ifndef TESTING
 #define TESTING  (default value)
#endif

#if TESTING==HOST
  ...
#elif TESTING==TARGET
 ...
#else
 ...
#endif

Alternative, maybe force a selection?:

#ifndef TESTING
 #error You must define a value for TESTING
#endif