None.
Defines a macro as in a #define preprocessor directive.
Not applicable.
Using the #define directive to define a macro name already defined by the -D option will result in an error condition.
The -Uname option, which is used to undefine macros defined by the -D option, has a higher precedence than the -Dname option.
The compiler configuration file uses the -D option to predefine several macro names for specific invocation commands. For details, see the configuration file for your system.
xlc myprogram.c -DCOUNT=100