#ifdef

If a keyword or variable is defined, then compile the following code.  This will not detect variables defined inside a library.

Syntax: #ifdef keyword or variable

Notes:

• When checking for a variable definition, the variable must be defined before the #ifdef directive

Example:

#ifdef testCode
  .....
#endif

Also See: #define, #undefine, #if, #ifndef, #else, #elseif, #endif