C Function pointers with parameter at declaration/ compile time - c

Question

Suppose we have a list of events (int) and actions (function pointers), as in:
typedef struct action_type {
int event;
int (*func)();
} action_type;
action_type actions[] = {
{ my_event1, my_action1 },
{ my_event2, my_action2 },
{ my_event3, my_action3 },
{ my_event4, my_action1 }
}
and i want to add conditions to actually running the action as part of the table, for
better readability and
simplification of the action functions.
action_type actions[] = {
{ my_event1, exceeds(&temperature, 100) , my_action1 },
{ my_event1, between(&temperature, 50, 80), my_action2 },
...
}
is there a way to get a notation like this?
Or would I need to create something like:
action_type actions[] = {
{ my_event1, $temperature, exceeds, 100, my_action1 },
...
}
However, this approach allows only a fixed number of parameters with a fixed type. As I am writing a library and conditions could be pretty much anything, I am looking for a way to allow different variable types and different parameter counts for the condition() function.
Edit: Added additional info on the conditions possibly having different numbers and types of parameters.

Answer 1

I'd use an X_MACRO, ie: something like this:
#define MY_EVENT_1 1
#define MY_EVENT_2 2
#define MY_EVENT_3 3
static int my_action1(void) { printf("Over 100!\n"); return 0; }
static int my_action2(void) { printf("Over 120!\n"); return 0; }
static int my_action3(void) { printf("Over 160!\n"); return 0; }
static int exceeds(int *val, int temp) { return *val > temp; }
typedef struct action_type {
int event;
int (*func)();
} action_type;
#define X_ACTIONS \
X(MY_EVENT_1, exceeds(&temperature, 100), my_action1) \
X(MY_EVENT_2, exceeds(&temperature, 120), my_action2) \
X(MY_EVENT_3, exceeds(&temperature, 160), my_action3)
static action_type actions[] = {
#define X(type, cond, cb) { type, cb },
X_ACTIONS
#undef X
};
int main() {
int temperature = 130;
#define X(type, cond, cb) if (cond) cb();
X_ACTIONS
#undef X
return 0;
}

Answer 2

you can do something like this
#define __NO__FUNC NULL
typedef unsigned char (*func)(void);
typedef unsigned char (*con)(unsigned char param1, unsigned char param2, unsigned char param3);
typedef struct {
int event
func custom_func;
con condition;
} action_type;
then use like this
action_type action[] = {
{ 1,SomeFunc, SomeCondition },
{ 2,__NO__FUNC,__NO__FUNC },
};
Where some func must retun unsigned char and have input type void such as
unsigned char SomeFunc(void)
{
// some logic
return 1;
}
unsigned char SomeCondition(unsigned char param1, unsigned char param2, unsigned char param3)
{
// logic
return 1;
}
and use it like this
if (action[0].condition(1,2,3)){
action[0].custom_func();
}
you can also check if a function is set with the following example:
if (action[0].condition(1,2,3)){
if(action[0].custom_func)
action[0].custom_func();
}
Example usage all together
unsigned char SomeFunc(void)
{
// some logic
return 1;
}
unsigned char SomeCondition(unsigned char param1, unsigned char param2, unsigned char param3)
{
// logic
return 1;
}
#define __NO__FUNC NULL
typedef unsigned char (*func)(void);
typedef unsigned char (*con)(unsigned char param1, unsigned char param2, unsigned char param3);
typedef struct {
int event
func custom_func;
con condition;
} action_type;
action_type action[] = {
{ 1,SomeFunc, SomeCondition },
{ 2,__NO__FUNC,__NO__FUNC },
};
void main(void)
{
unsigned char temperature = 0;
unsigned char val = 30;
unsigned char another_val = 50;
if (action[0].condition(temperature ,val,another_val )){
action[0].custom_func();
}
}
UPDATE : I have added a second function parameter, called condition which can be used to check a output before executing custom_func()
UPDATE 2 : Added the condition function to accept variables as input
UPDATE 3 : I have added a example code of how to use it, however i like to point out that in your question you cannot have a variable number of arguments inside the declaration of those functions. The C syntax does not allow that.
An element is created inside the struct of type " typedef unsigned char (*con)(unsigned char param1, unsigned char param2, unsigned char param3);
"
Meaning that those element accepts a function that returns unsigned char and has a input of (unsigned char param1, unsigned char param2, unsigned char param3);
You cannot add functions that have different return type or different parameters.
Hope it helps!
Best regards