How to separate #defined arguments in C - c

Question

I'm working on an embedded project and I have all the ports and pins defined like this:
#define SENSOR_1 gpioPortA,15
Is there a way to extract just the integer without creating a new #define?
So far I used a typedef and assigned the pin value from the #define like so:
typedef struct
{
GPIO_Port_TypeDef port;
uint8_t pin;
}sensor_t;
sensor_t sensor1 = {SENSOR_1};
/* Now sensor1.pin is the pin value */
but I want to pass the pin to a switch case and I can only use constant values for that and I'd rather avoid using an if statement.
Is there a way to pass the pin to a switch case without a new #define?

Answer 1

Short answer is no.
You could however use sensor1.pin when needed but not in case of switch statement as switch does not support variables there. In this case use if-else statement.
Or do it like this:
#define SENSOR_1_PIN 10
#define SENSOR_1 my_port,SENSOR_1_PIN
and then in switch you use SENSOR_1_PIN in case part.
switch (condition) {
case SENSOR_1_PIN:
//Do stuff
break;
//....
}
Just to remind again as it was posted in first comment on your question. Doing that is very dangerous.
Most proper way would be to do it like this:
#define SENSOR_1_PORT GPIOB
#define SENSOR_1_PIN 15
//If structure order changes here, you may lead to wrong data interpretation
sensor_t sensor1 = {SENSOR_1_PORT, SENSOR_1_PIN};
If you are C99 compliant, you may do it even more safer like this:
//If structure order changes here, your data are still properly assigned to fields
sensor_t sensor1 = {.port = SENSOR_1_PORT, .pin = SENSOR_1_PIN};

Answer 2

You can define a macro to extract the value from your definition.
#define GET_SECOND(x, y) y
#define PIN_VALUE(x) GET_SECOND(x)
switch (pin) {
case PIN_VALUE(SENSOR_1):
/* ... */
break;
}
PIN_VALUE must allow SENSOR_1 to be expanded via helper macro so that the second part can be extracted.

Answer 3

The proper solution at this point is to re-design the definitions into something that makes more sense, or alternatively create new constants.
As a last resort, if you are stuck with these macros, you can parse them in the following way:
#include <stdio.h>
#include <stdint.h>
typedef int GPIO_Port_TypeDef; // whatever type this happens to be
typedef struct
{
GPIO_Port_TypeDef port;
uint8_t pin;
}sensor_t;
#define GET_FIELD(field,...) (sensor_t){__VA_ARGS__}.field
#define SENSOR_1 gpioPortA,15
int main (void)
{
int gpioPortA = 1;
printf("%d %d", GET_FIELD(port, SENSOR_1), GET_FIELD(pin, SENSOR_1));
}
The type-generic version would be:
#define GET_FIELD(type, field, ...) (type){__VA_ARGS__}.field
...
printf("%d %d", GET_FIELD(sensor_t, port, SENSOR_1), GET_FIELD(sensor_t, pin, SENSOR_1));
This scales variably no matter how many fields there are. This is however not recommended practice. Macros in general, and variadic macros in particular, should be avoided.
As for how to use run-time variables in case - you can't. Use an if-else if statement instead.

Answer 4

What about inserting a define inside a define ? Instead of directly adding 15, you could make a define holding 15 and insert it elsewhere.
E.g:
#define SENSORVAL 15
#define SENSOR_1 gpioPortA,SENSORVAL
typedef struct
{
GPIO_Port_TypeDef port;
uint8_t pin;
}sensor_t;
sensor_t sensor1 = {SENSOR_1};
/* Now sensor1.pin is the pin value */