将宏参数传递给带逗号的函数

Question

In the MSP430 world, the driverlib has functions for working with GPIO pins:

GPIO_SetAsInputPin(port, pin)

I would like a single macro to define a single pin, for example:

#define PB1     (GPIO_PORT_P2, GPIO_PIN4)
#define PB2     (GPIO_PORT_P2, GPIO_PIN5)

When I call the function with the macro:

GPIO_setAsInputPin(PB1);

I get a too few arguments in function call error. Is there a different way of making this work?

Answer 1

The parentheses around the expansion of PB1 make it into a single argument with a comma operator in between — so your invocation expands to:

GPIO_setAsInputPin((GPIO_PORT_P2, GPIO_PIN4))

You should probably use:

#define PB1   (GPIO_PORT_P2), (GPIO_PIN4)

which expands to:

GPIO_setAsInputPin((GPIO_PORT_P2), (GPIO_PIN4))

giving you two arguments. Or you could omit the parentheses around the names and you'd probably be safe.

You may still have problems if GPIO_setAsInputPin is itself a macro that expects two arguments. Then you'd need something like:

#define GPIO_setAsInputPin_1(x)    GPIO_setAsInputPin(x)

and you would invoke:

GPIO_setAsInputPin_1(PB1);

and you'd get as output:

GPIO_setAsInputPin((GPIO_PORT_P2), (GPIO_PIN4));

or whatever the underlying macro expands to.