Executes initialization processing for referencing variable arguments.
void va_start (va_list ap, parmN);
ap Variable for accessing variable arguments
parmN Identifier of rightmost argument
The va_start macro initializes ap for subsequent use by the va_arg and va_end macros.
The argument parmN is the identifier of the rightmost argument in the argument list in the external function definition (the one just before the , ...).
To reference variable unnamed arguments, the va_start macro call must be executed first of all.