C Preprocessor generate macros by concatenation and stringification [duplicate] - c

Question

This question already has answers here:
What are the applications of the ## preprocessor operator and gotchas to consider?
(13 answers)
Closed 7 years ago.
I have a set of target macros for which I want to generate aliases based on a choosing macro, like so:
Choosing macro:
#define I2C_MODULE 1
Alias macros (conceptual form):
#define I2C_MODULE_BASE I2C<Value of I2C_MODULE>_BASE
#define I2C_MODULE_NVIC INT_I2C<Value of I2C_MODULE>
Target macros (from an external file out of my control):
#define INT_I2C0 24
#define INT_I2C1 53
...
#define I2C0_BASE 0x40020000
#define I2C1_BASE 0x40021000
...
I wanted to have the preprocessor generate the alias macros I2C_MODULE_BASE and I2C_MODULE_NVIC based on the
choosing macro I2C_MODULE, but after much reading Q1, P1 and many other references I lost track of, I ended up hard-coding their values. Below I show my current working definitions, and then my last failed attempts at generating the macros:
What works:
#define I2C_MODULE 1
#define I2C_MODULE_BASE I2C1_BASE
#define I2C_MODULE_NVIC INT_I2C1
what did not work:
#define I2C_MODULE 1
#define STR_HELPER(x) #x
#define STR(x) STR_HELPER(x)
/* Attempt 1 */
#define I2C_MODULE_BASE "I2C" STR(I2C_MODULE) "_BASE"
#define I2C_MODULE_NVIC "INT_I2C" STR(I2C_MODULE)
/* Attempt 2 */
#define _I2C_MODULE_BASE "I2C" STR(I2C_MODULE) "_BASE"
#define _I2C_MODULE_NVIC "INT_I2C" STR(I2C_MODULE)
#define I2C_MODULE_BASE _I2C_MODULE_BASE
#define I2C_MODULE_NVIC _I2C_MODULE_NVIC
EDIT: I expanded upon the accepted answer to get to where I wanted, as follows:
#define PASTE2(a, b) a ## b
#define PASTE3(a, b, c) a ## b ## c
#define _I2C_MODULE_BASE(x) PASTE3(I2C, x, _BASE)
#define _I2C_MODULE_NVIC(x) PASTE2(INT_I2C, x)
#define I2C_MODULE_BASE _I2C_MODULE_BASE(I2C_MODULE)
#define I2C_MODULE_NVIC _I2C_MODULE_NVIC(I2C_MODULE)

Answer 1

This seems to work:
#define I2C_MODULE 1
//Alias macros (conceptual form):
//#define I2C_MODULE_BASE I2C<Value of I2C_MODULE>_BASE
//#define I2C_MODULE_NVIC INT_I2C<Value of I2C_MODULE>
//Target macros (from an external file out of my control):
#define INT_I2C0 24
#define INT_I2C1 53
#define I2C0_BASE 0x40020000
#define I2C1_BASE 0x40021000
#define PASTE2(a, b) a ## b
#define PASTE3(a, b, c) a ## b ## c
#define I2C_MODULE_BASE(x) PASTE3(I2C, x, _BASE)
#define I2C_MODULE_NVIC(x) PASTE2(INT_I2C, x)
extern int i2c_module_base = I2C_MODULE_BASE(I2C_MODULE);
extern int i2c_module_nvic = I2C_MODULE_NVIC(I2C_MODULE);
extern int i2c_module_base_0 = I2C_MODULE_BASE(0);
extern int i2c_module_nvic_0 = I2C_MODULE_NVIC(0);
extern int i2c_module_base_1 = I2C_MODULE_BASE(1);
extern int i2c_module_nvic_1 = I2C_MODULE_NVIC(1);
Sample output (from cpp):
# 1 "xx.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "xx.c"
# 21 "xx.c"
extern int i2c_module_base = 0x40021000;
extern int i2c_module_nvic = 53;
extern int i2c_module_base_0 = 0x40020000;
extern int i2c_module_nvic_0 = 24;
extern int i2c_module_base_1 = 0x40021000;
extern int i2c_module_nvic_1 = 53;
It is closely based on my answer to C preprocessor and token concatenation.
There are undoubtedly other ways that the I2C_MODULE_BASE and I2C_MODULE_NVIC macros could be written, but the key points are:
Using the ## token pasting operator (not the # stringifying operator).
Using two levels of macro (for example, I2C_MODULE_BASE and PASTE3).

Answer 2

I suspect that you are writing a I2C driver which can generically handle multiple I2C hardware peripherals in the same micro-controller without rewriting all the same code multiple times.
In that case, what you are really looking for probably is something like this:
#define I2C1 ((volatile uint8_t*)0x12345678) // address of first hw register for I2C1
#define I2C2 ((volatile uint8_t*)0x55555555) // address of first hw register for I2C2
/* map all registers used for I2C, they will have same register layout for every
peripheral no matter which one: */
#define I2C_CONTROL(base) (*(base + 0))
#define I2C_DATA(base) (*(base + 1))
...
// create some dummy typedef to make your functions look nice:
typedef volatile uint8_t* I2C_t;
// define whatever functions you need in the driver:
void i2c_init (IC2_t bus);
void i2c_send (I2C_t bus, const uint8_t* data, size_t n);
...
// implement functions in a bus-independent way:
void i2c_init (IC2_t bus)
{
I2C_CONTROL(bus) = THIS | THAT; // setup registers
}
// caller code:
i2c_init(I2C1);
i2c_init(I2C2);
...
i2c_send(I2C1, "hello", 5);
i2c_send(I2C2, "world", 5);

Answer 3

Just use #if / #else / #endif
#if (I2C_MODULE == 0)
#define I2C_MODULE_BASE I2C0_BASE
#define I2C_MODULE_NVIC INT_I2C0
#elif (I2C_MODULE == 1)
#define I2C_MODULE_BASE I2C1_BASE
#define I2C_MODULE_NVIC INT_I2C1
#else
#error Unknown configuration
#endif