The #define directive is used to define values for substitution and
for #ifdef directives (section 
).
Values defined using an #define directive are substituted into
the input file when the value found.
The syntax for a #define directive is:
#define Name Value
where Name is a character string, and Value is a
character string, integer, or floating point value.
The defined value will be substituted into the file
where ever Name is encountered. Name can
also be used in #ifdef directives.
When the command line option -v Name Value is used, values are defined in this
way.
If the syntax #define Name is used for the directive, then the Name is defined for use with #ifdef directives only. When the command line option -d Name is used, values are defined in this way. Use of Name outside of an #ifdef directive will result in NAME_DEFINED_WITHOUT_A_VALUE will be substituted in for the Name.
Using the #define directive, the code
/* define_example.inp */ #define ENERGY 100 // define a value #define ETEMP 10 // define another value #define EMARGIN 1.1 // define yet another value #define ECUT ENERGY*EMARGIN // define a value in terms of other defines for input e=ENERGY with margin EMARGIN the cut off is ECUT note the mathematical operations of: addition: ETEMP+EMARGIN subtraction: ETEMP-EMARGIN multiplication: ETEMP*EMARGIN division: ETEMP/EMARGIN Note, division is not allowed since it would be confused with the LAHET end of line character/ #define TEST_VALUE // a value that should exist only for an ifdef TEST_VALUE was not defined with a value.expands out to
for input e=100 with margin 1.1 the cut off is 110.000000 note the mathematical operations of: addition: 11.100000 subtraction: 8.900000 multiplication: 11.000000 division: 10/1.1 Note, division is not allowed since it would be confused with the LAHET end of line character/ TEST_VALUE_DEFINED_WITHOUT_A_VALUE was not defined with a value.
Unlike the c and C++ preprocessors, the #define directive in this preprocessor cannot be used to define macros.