Say my code looks like this:
gpios.h:
#define GPIO_BASE 0x08000100
#define GPIOA ((GpioRegs *) (GPIO_BASE + 0x04))
#define GPIOB ((GpioRegs *) (GPIO_BASE + 0x0C))
#define GPIOC ((GpioRegs *) (GPIO_BASE + 0x14))
switches.h:
#define SWITCH1_PORT GPIOA // On this particular system, both switches
#define SWITCH2_PORT GPIOA // are on the same port. This could change in the future
switches.c:
#if SWITCH1_PORT == SWITCH2_PORT
// Code is a lot simpler if both switches are on the same port
#else
// Otherwise do it the hard way
#endif
SWITCH1_PORT and SWITCH2_PORT are both constants at compile time, so comparing them at compile time should be valid, but in practice I get this error message:
gpios.h:772:45: error: operator '*' has no right operand
772 | #define GPIOA ((GpioReg *) (GPIO_BASE + 0x04))
| ^
switches.h:102:33: note: in expansion of macro 'GPIOA'
102 | #define SWITCH1_PORT GPIOA
| ^~~~~
switches.c:172:5: note: in expansion of macro 'SWITCH1_PORT'
172 | #if SWITCH1_PORT == SWITCH2_PORT
| ^~~~~~~~~~~~
I tried casting the pointers to uint32_t, and I tried defining a COMPARE_POINTERS macro, but nothing helped.
Is there a way to do what I want here?
3
If you expand the macros, you can see why it doesn’t work as expected:
#if ((GpioRegs *) (GPIO_BASE + 0x04)) == ((GpioRegs *) (GPIO_BASE + 0x04))
AFAIK, you can’t do type-casts inside of an #if. You are likely going to have to make a different set of macros that resolve to integers instead of pointers, eg:
gpios.h:
#define GPIO_BASE 0x08000100
#define GPIOA_INT (GPIO_BASE + 0x04)
#define GPIOB_INT (GPIO_BASE + 0x0C)
#define GPIOC_INT (GPIO_BASE + 0x14)
#define GPIOA ((GpioRegs *) GPIOA_INT)
#define GPIOB ((GpioRegs *) GPIOB_INT)
#define GPIOC ((GpioRegs *) GPIOC_INT)
switches.h:
#define SWITCH1_PORT_INT GPIOA_INT
#define SWITCH2_PORT_INT GPIOA_INT
#define SWITCH1_PORT GPIOA
#define SWITCH2_PORT GPIOA
switches.c:
#if SWITCH1_PORT_INT == SWITCH2_PORT_INT
// Code is a lot simpler if both switches are on the same port
#else
// Otherwise do it the hard way
#endif
6