Defining a function pointer
To define a pointer to a function that
has no arguments and no return value, you say:
void (*funcPtr)();
When you are looking at a
complex definition like this, the
best way to attack it is to start in the middle and work your way out.
“Starting in the middle” means starting at the variable name, which
is funcPtr. “Working your way out” means looking to the right
for the nearest item (nothing in this case; the right parenthesis stops you
short), then looking to the left (a pointer denoted by the asterisk), then
looking to the right (an empty argument list indicating a function that takes no
arguments), then looking to the left (void, which indicates the function
has no return value). This right-left-right motion works with most
declarations.
To review, “start in the
middle” (“funcPtr is a ...”), go to the right (nothing
there – you're stopped by the right parenthesis), go to the left and find
the ‘*’ (“... pointer to a ...”), go to the right
and find the empty argument list (“... function that takes no arguments
... ”), go to the left and find the void (“funcPtr is
a pointer to a function that takes no arguments and returns
void”).
You may wonder why *funcPtr
requires parentheses. If you didn't use them, the compiler would
see:
void *funcPtr();
You would be declaring a function (that
returns a void*) rather than defining a variable. You can think of
the compiler as going through the same process you do when it figures out what a
declaration or definition is supposed to be. It needs those parentheses to
“bump up against” so it goes back to the left and finds the
‘*’, instead of continuing to the right and finding the empty
argument list.
