The following syntax is used to define a macro with parameters:

#define macro_identifier(<arg_list>) token_sequence

Any comma within parentheses in an argument list is treated as part of the argument, not as an argument delimiter. 

Note there can be no whitespace between the macro identifier and the (. The optional arg_list is a sequence of identifiers separated by commas, not unlike the argument list of a C function. Each comma-delimited identifier plays the role of a formal argument or placeholder. 

Such macros are called by writing

macro_identifier<whitespace>(<actual_arg_list>)

in the subsequent source code. The syntax is identical to that of a function call; indeed, many standard library C "functions" are implemented as macros. However, there are some important semantic differences, side effects, and potential pitfalls. 

The optional actual_arg_list must contain the same number of comma-delimited token sequences, known as actual arguments, as found in the formal arg_list of the #define line: There must be an actual argument for each formal argument. An error will be reported if the number of arguments in the two lists is different. 

A macro call results in two sets of replacements. First, the macro identifier and the parenthesis-enclosed arguments are replaced by the token sequence. Next, any formal arguments occurring in the token sequence are replaced by the corresponding real arguments appearing in the actual_arg_list. 

As with simple macro definitions, rescanning occurs to detect any embedded macro identifiers eligible for expansion.