C macro : turn a number into a string

Question

I have a table that defines symbols appearance on a 5x7 dot display. Something like:

extern UINT8 symbols[][5] = {
    {0x0,0x0,0x0,0x0,0x0},
    {0x0,0x0,0x5F,0x0,0x0},
    {0x0,0x7,0x0,0x7,0x0},
    {0x14,0x7F,0x14,0x7F,0x14}, // etc.

The leading part of the table matches ASCII table, followed by a set of special symbols, e.g. an arrow, or a check-mark. To reference those I have a list of macros:

#define SYMBOL_LEFT_ARROW 120 // 120 is the entry in the table
#define SYMBOL_RIGHT_ARROW (SYMBOL_LEFT_ARROW+1)    
#define SYMBOL_UP_ARROW (SYMBOL_RIGHT_ARROW+1)

Now I need to say something like (won't compile):

const char * const message = "Next" + SYMBOL_RIGHT_ARROW;

Question: How do I turn SYMBOL_RIGHT_ARROW into "\x79", or whole string into "Next\x79" AT COMPILE TIME so I can have the string in R/O section?

Freescale HC08 C-compiler.

I would try to avoid any run-time string making: 1) extra cycles; 2) I'd like to keep const strings in ROM (it's an embedded system). — THX-1138
– THX-1138, Commented Oct 20, 2009 at 15:55
Same question in C++: stackoverflow.com/questions/6713420. See also stackoverflow.com/questions/75352154/… — user202729
– user202729, Commented Aug 28 at 2:51

pmg · Accepted Answer · 2009-10-21 19:18:36Z

You can concatenate strings in C source:

printf("%s\n", "forty" "two"); /* prints "fortytwo" */
/* NOTE:             ^^^ no punctuation */

To do that with your symbols is a lot of work, but maybe you can live with that.

#define SYMBOL_LEFT_ARROW 120
#define SYMBOL_LEFT_ARROW_STR "\x79"
#define SYMBOL_RIGHT_ARROW (SYMBOL_LEFT_ARROW + 1)
#define SYMBOL_RIGHT_ARROW_STR "\x83"
const char * const message = "Next" SYMBOL_RIGHT_ARROW_STR;

UPDATE

If you can make the value of the symbol match its position in the symbol table (120 match "\x78"), try these macros

#include <stdio.h>

#define ADD_ZERO_X(y) 0x ## y
#define SYMBOL_NUM(x) ADD_ZERO_X(x)

#define STRINGIZE(z) #z
#define ADD_SLASH_X(y) STRINGIZE(\x ## y)
#define SYMBOL_STR(x) ADD_SLASH_X(x)

#define SYMBOL_LEFT_ARROW 78 /* must write in hexadecimal without any prefix */
#define SYMBOL_RIGHT_ARROW 79
#define SYMBOL_UP_ARROW 7a

int main(void) {
  printf("%d\n", SYMBOL_NUM(SYMBOL_LEFT_ARROW));
  printf("%s\n", SYMBOL_STR(SYMBOL_LEFT_ARROW));
  printf("%d\n", SYMBOL_NUM(SYMBOL_RIGHT_ARROW));
  printf("%s\n", SYMBOL_STR(SYMBOL_RIGHT_ARROW));
  printf("%d\n", SYMBOL_NUM(SYMBOL_UP_ARROW));
  printf("%s\n", SYMBOL_STR(SYMBOL_UP_ARROW));
  return 0;
}

Edit (SO doesn't like my browser)

After macro expansion SYMBOL_NUM(32) is transformed to a integer literal (0x78); and SYMBOL_STR(78) is transformed to a string literal ("\x78").

You can use the literals as if you had typed them in.

const char *test = "Next" SYMBOL_STR(78) " one";
/* same as
   const char *test = "Next\x78 one";
*/

steve alexander · Accepted Answer · 2009-10-20 19:04:03Z

3

I came up with this little program:

#include <stdio.h>

#define TEST_CHR '\x77'
#define VAL(x) #x
#define STRINGIFY(x) VAL(x)
int main()
{
   int x = TEST_CHR;
   char *yyy = "%d " STRINGIFY(TEST_CHR) "\n";

   printf(yyy,x);

   return 0;

}

the indirection in the macro is necessary so that your character gets expanded before the "#" turns it into a string. notice that the '\x77' value turns into a valid int when you use it that way...

answered Oct 20, 2009 at 19:04

steve alexander

311 bronze badge

4 Comments

THX-1138 Over a year ago

How do I make '\x77' from #define MY_SYMBOL 0x77?

Joseph Garvin Over a year ago

#MY_SYMBOL will make "\x77" but not '\x77'.

steve alexander Over a year ago

i think '\x77' will take the place of 0x77 in int expressions? (thus the assignment of "x" in main)...

steve alexander Over a year ago

also, i think: char my_literal[] = {"Next" STRINGIFY(TEST_CHR)}; // should be romable...

THX-1138 · Accepted Answer · 2009-10-20 15:56:40Z

2

This is best I could come up with, not perfect, but can be put in ROM:

const char message[] = {'N','e','x','t',SYMBOL_RIGHT_ARROW,EOS};

answered Oct 20, 2009 at 15:56

THX-1138

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