Use macro with token-pasting operator

Question

I am facing a problem while making a code more general, I want to replace hardcoded values with macro but I am facing this issue :

Original code :

#define io_dir_in(port, pin) NRF_P##port->PIN_CNF[pin] = (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos) + (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos)

io_dir_in(0, 0);

I added :

#define A_Port  0
#define A_Pin   0

And replaced :

io_dir_in(A_Port, A_Pin);

But I get the error identifer "NRF_PA_Port" is undefined because NRF_P and A_Port are getting concatenated.
Anyway to make it work ?

This is kind of a duplicate of this: https://stackoverflow.com/questions/16989730/stringification-how-does-it-work. # and ## work the same in terms of expansion. — Lundin, Sep 20 '21 at 14:17

score 1 · Accepted Answer · answered Sep 20 '21 at 11:59

The problem is that "concatenation of tokens" is done before an expansion of tokens. You need to add an extra step of expansion in between.

#define io_dir_in_impl(port, pin) NRF_P##port->PIN_CNF[pin] = (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos) + (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos)
#define io_dir_in(port, pin) io_dir_in_impl(port, pin)

Now before io_dir_in_impl() is expanded all its arguments are expanded. Thus A_Port will be replaced with 0.

With this tweak io_dir_in(A_Port, A_Pin); expands as:

NRF_P0->PIN_CNF[0] = (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos) + (GPIO_PIN_CNF_INPUT_Connect << GPIO_PIN_CNF_INPUT_Pos);

Use macro with token-pasting operator

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