Preprocessor string pasting fun

Hi guys, my first post here.

I'm having trouble doing string concatenation at the preprocessor level.

This works fine :

Code:

---

#define A "TOKEN1" "TOKEN2"

---

and this also works fine:

Code:

---

#define A "TOKEN1"
#define B "TOKEN2" A

---

but this refuses to compile :

Code:

---

#define A "TOKEN1" __FUNCTION__

---

The only difference seems to be that __FUNCTION__ is a builtin.

Is there any other way to do this kind of concatenation? It's important that this happens on the preprocessor. BTW, this is with g++ 3.2.

Thanks in advance!

Are you putting the definition inside of a function?

Code:

---

#include <stdio.h>

void foo(void)
{
#define A "TOKEN1" __FUNCTION__
  puts(A);
}

int main(void)
{
  foo();
  return 0;
}

/* my output
TOKEN1foo
*/

---

Yes. I investigated a little further, and came to this : the following code

Code:

---

#define FOOBAR const char* __fnname = __FUNCTION__ "A";
#define QUUX const char* __fnname = __FILE__ "A";

int main (void)
{
        FOOBAR
        QUUX
       
        return 1;
}

---

is preprocessed as

Code:

---

# 1 "test.cpp"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "test.cpp"

int main (void)
{
        const char* __fnname = __FUNCTION__ "A";
        const char* __fnname = "test.cpp" "A";

        return 1;
}

---

As you can see, __FILE__ is expanded by the preprocessor but __FUNCTION__ isn't (maybe it makes sense...). If I put __FUNCTION__ inside main() instead of through a macro the result is the same :(

Sorry for the confusion. "If I put __FUNCTION__ inside main() instead of through a macro the result is the same" meant yes.

Anyway, I now believe there's no solution - concatenating __FUNCTION__ with a string literal seems to be deprecated, as mentioned vaguely in some mailing lists.

Thanks anyway...

There's good reason that is no longer supported nor...hopefully...used.

Quote:

---

Originally Posted by Bubba

There's good reason that is no longer supported nor...hopefully...used.

---

And what is that reason?

Why are ypu compiling your C code as C++? Or, why ask a C++ question on a C board? Different compilers do things differently.

If you are in fact using C and not C++, compile it that way. Also, if indeed that is true, C99 introduces a predefined identifier called __func__.

Quote:

---

C: A Reference Manual, 5th Edition
Pages 23 and 24.

2.6.1 Predefined Identifiers

Although not a keyword, C99 introduces the concept of a predefined identicier and defines
one such: __func__. Unlike a predefined macro, a predefined identifier can follow nor-
mal block scoping rules. Like keywords, predefined identifiers must not be defined by
programmers.

The identifier __func__ is implicitly declared by C99 implementations as if the
following declaration appeared after the opening brace of each function definition:

Code:

---

static const char __func__[] = "function-name";

---

This identifier could be used by debugging tools to peint out the name of the enclosing
function, as in:

Code:

---

if (failed) printf("Function %s failed\n", __func__ );

---

When translating C programs for targets with tight memory constraints, C implementa-
tions will have to be careful about getting rid of these strings if they are not needed at run-
time.

---

Quzah.