Joining and expanding #defines

Hi rtsh,

you can do that in effect but not like that

int i =strlen(one);
i += strlen(two);

char * a = (char *)calloc (i+1);
strcpy (a,one);
strcat(a,two);

now you can use a as a concatenated value

Sunnycoder

rtsh,

> and i should end up with the value in location 0x12345678
that may not be necessarily possible ... you can try to write to that location but most likely you will end up getting a segfault

Sunnycoder

Sunnycoder:

Re the segfault - I'm well aware... was just an example.  

I really don't like the strcpy method - there must be a way to do this preprocessor?

I can join defines with ##, but I can't seem to force the order so that they're evaluated prior to the catenation - I'd just get onetwo, which doesn't exist...

Hi rtsh,

Using the preprocessor,you can't do that.

>but I can't seem to force the order so that they're evaluated prior to the catenation - I'd >just get onetwo, which doesn't exist

Precisely why.

#defines cannot be forced to evaluate before the substitution.

I've finally found the answer - see:

http://tigcc.ticalc.org/doc/cpp.html#SEC28 which says:

"Macros that call other macros that stringify or concatenate:

If an argument is stringified or concatenated, the prescan does not occur. If you want to expand a macro, then stringify or concatenate its expansion, you can do that by causing one macro to call another macro that does the stringification or concatenation. For instance, if you have

#define AFTERX(x) X_ ## x
#define XAFTERX(x) AFTERX(x)
#define TABLESIZE 1024
#define BUFSIZE TABLESIZE

then AFTERX(BUFSIZE) expands to X_BUFSIZE, and XAFTERX(BUFSIZE) expands to X_1024. (Not to X_TABLESIZE. Prescan always does a complete expansion.) "

(Can an admin close this now I've found the answer?)