Nested preprocessors to equate to a #define

Question

I am trying to create a macro that coverts a #define create in the makefile to an autogenerated list of #defines which are starting address to peripheral components. Here is the test code:

#include <stdio.h>
#include <stdint.h>

/* Created by makefile to specify the core/CPU */
#define  CPU_ID       5

/* Autogenerated hardware register descriptors */
#define CPU0_PERIPHERAL_I2C_BASE__ADDR         (0x40000)
#define CPU1_PERIPHERAL_I2C_BASE__ADDR         (0x56000)
#define CPU2_PERIPHERAL_I2C_BASE__ADDR         (0x57000)
#define CPU3_PERIPHERAL_I2C_BASE__ADDR         (0x61000)
#define SUBCORE0_PERIPHERAL_I2C_BASE__ADDR     (0x67000)
#define SUBCORE1_PERIPHERAL_I2C_BASE__ADDR     (0x90000)
#define SUBCORE2_PERIPHERAL_I2C_BASE__ADDR     (0xA3000)
#define SUBCORE3_PERIPHERAL_I2C_BASE__ADDR     (0xE3000)

#define BASE_ADDR_DEF     _PERIPHERAL_I2C_BASE__ADDR

/* defines for translating CPU_ID into autogenerated hardware regs */
#define CPU_ID_0       "CPU0"
#define CPU_ID_1       "CPU1"
#define CPU_ID_2       "CPU2"
#define CPU_ID_3       "CPU3"
#define CPU_ID_4       "SUBCORE0"
#define CPU_ID_5       "SUBCORE1"
#define CPU_ID_6       "SUBCORE2"
#define CPU_ID_7       "SUBCORE3"

#define _JOIN(x,y)       x ## y
#define _DEF1(cpu_id)    _JOIN(CPU_ID_,cpu_id)
#define _DEF2(cpu_id)    _JOIN(_DEF1(cpu_id),BASE_ADDR_DEF)

int main(void)
{
    printf("%s\n", _DEF1(CPU_ID));  // <- this prints out "SUBCORE0" which is part of the way there
    printf("%X\n", _DEF2(CPU_ID));  // <- This will not compile
    return 0;
}

The _DEF1 macro sort of works at the output, in this case, will be "SUBCORE1" as I expect. I can't seem to get the macro to translate up one additional level to combine the "SUBCORE1" with "_PERIPHERAL_I2C_BASE__ADDR" to create "SUBCORE1_PERIPHERAL_I2C_BASE__ADDR" then print out the hex value which should be 0x90000. Am I missing another level of macros during the expansion that I am not seeing or can't get correct?

Edit: I know people are commenting about the literal strings and I know this wasn't the end goal, but this was just one of many iterative steps while experimenting. I just needed some sort of example to show what I was trying to do. Thanks.

Answer 1

1. Declare macros not as string literals. Just as strings. Change ex. "SUBCORE3" to SUBCORE3. Preprocessor can't remove ".
2. You need to trigger expansion with a nested macro. Ex. #define _JOIN2(x, y) x ## y and then #define _JOIN(x, y) _JOIN2(x, y)
3. All identifiers starting with a underscore followed by big letter are reserved by standard. Declaring them is undefined behavior.

#include <stdio.h>
#include <stdint.h>

/* Created by makefile to specify the core/CPU */
#define  CPU_ID       5

/* Autogenerated hardware register descriptors */
#define CPU0_PERIPHERAL_I2C_BASE__ADDR         (0x40000)
#define CPU1_PERIPHERAL_I2C_BASE__ADDR         (0x56000)
#define CPU2_PERIPHERAL_I2C_BASE__ADDR         (0x57000)
#define CPU3_PERIPHERAL_I2C_BASE__ADDR         (0x61000)
#define SUBCORE0_PERIPHERAL_I2C_BASE__ADDR     (0x67000)
#define SUBCORE1_PERIPHERAL_I2C_BASE__ADDR     (0x90000)
#define SUBCORE2_PERIPHERAL_I2C_BASE__ADDR     (0xA3000)
#define SUBCORE3_PERIPHERAL_I2C_BASE__ADDR     (0xE3000)

#define BASE_ADDR_DEF     _PERIPHERAL_I2C_BASE__ADDR

/* defines for translating CPU_ID into autogenerated hardware regs */
#define CPU_ID_0       CPU0
#define CPU_ID_1       CPU1
#define CPU_ID_2       CPU2
#define CPU_ID_3       CPU3
#define CPU_ID_4       SUBCORE0
#define CPU_ID_5       SUBCORE1
#define CPU_ID_6       SUBCORE2
#define CPU_ID_7       SUBCORE3

// usually those are called CONCAT or CONCATX or CONCAT2 or XCONCAT etc.
// so I name them the same here
// XCONCAT is a mnemonic from "eXpand then CONCATenate"
#define CONCAT(x,y)     x ## y
#define XCONCAT(x,y)    CONCAT(x, y)
#define STRING(x)        #x
#define XSTRING(x)       STRING(x)
// note that glibc defines __CONCAT __XCONCAT __STRING __XSTRING

// trigger the expansions
#define DEF1(cpu_id)    XCONCAT(CPU_ID_, cpu_id)
#define DEF2(cpu_id)    XCONCAT(DEF1(cpu_id),BASE_ADDR_DEF)

int main(void)
{
    printf("%s\n", XSTRING(DEF1(CPU_ID)));  // <- this prints out "SUBCORE0", which is at all not part the way here
    printf("%X\n", DEF2(CPU_ID));  // <- This will expand to 0x90000
    return 0;
}