Is this like function call arguments are defined in the BNF grammar?

Question

Reading this C's BNF grammar I didn't understand which part this:

| postfix_exp '(' argument_exp_list ')'
| postfix_exp '('           ')'

does handle also a function call like id(exp, exp) and id(). Is this the single combination valid in C syntax or I'm missing something? if so, why not just:

| id '(' argument_exp_list ')'
| id '('            ')' 

Answer 1

The BNF grammar id '(' argument_exp_list ')' is actually equivalent to postfix_exp '(' argument_exp_list ')' where postfix_exp can be a primary_exp as stated on its l-value.

postfix_exp     : primary_exp
                | postfix_exp '[' exp ']'
                | postfix_exp '(' argument_exp_list ')'
                | postfix_exp '('           ')'
                | postfix_exp '.' id
                | postfix_exp '->' id
                | postfix_exp '++'
                | postfix_exp '--'

where primary_exp is:

primary_exp     : id
                | const
                | string
                | '(' exp ')'