Whitespaces before macro bracket

I believe I read somewhere that you should always align the preprocessor # in the first column, but now I'm having trouble verifying my sources. I googled, but didn't find any real good info. Is there a rule or recommendation on placing whitespaces before the bracket? Or immediately after, for that matter. I've seen different constructs:

Code:

---

#ifdef FOO
 #include "foo.h"
#endif

---

Code:

---

#ifdef FOO
# include "foo.h"
#endif

---

The reason I'm asking is that I've started using the following approach when it comes to debugging:

Code:

---

#ifdef DEBUG
printf("Test print: foo");
#endif

---

Deep inside functions, this would look a bit bizarre if I have to keep the macros in the first column. If that's the recommendation though, I will of course adapt. There must be a succinct guideline for this somewhere - please point me in the right direction!

Thanks!
-tretton

Leading indentation before a # is a style issue.
Like all style issues, there are some good arguments for both sides.

Instead of using #define,

Code:

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const bool DEBUG = true;

---

Then you could use an if statement nested deep as you want
without worrying about preprocessor formatting.

EDIT: Sorry, I'm not sure const is even part of C. If it's not my apologies, I guess I really am a C++ guy.

Maybe try this:

Code:

---

#define DEBUG 1

---

...and do the if test as I said above. Then to turn off debugging change it to 0.

Quote:

---

I believe I read somewhere that you should always align the preprocessor # in the first column

---

I was under this impression also, but a quick check of the C89 draft says this:

Quote:

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A preprocessing directive consists of a sequence of preprocessing tokens that begins with a # preprocessing token that is either the first character in the source file (optionally after white space containing no new-line characters) or that follows white space containing at least one new-line character, and is ended by the next new-line character.

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It appears that it was a requirement of some pre-ansi preprocessors. GCC can still be instructed to use this requirement by using the -traditional flag.

Many programmers put the indentation between the # and the command:

Code:

---

#if defined(DEBUG)
#    include <debug.h>
#    if defined(SUPER_DEBUG)
#        include <super_debug.h>
#    endif
#endif

---

Even if it is not required, this can be good style as it enables the preprocessor commands to be easily spotted by scanning down the first column.

I still put my #ifdef DBG stuff starting in column 1. As Salem says it is a style issue, but for me, when I have a ton of code, if I want to comment out some debug statements, they are right there in column 1.

Your mileage may vary, of course.

Quote:

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Originally Posted by tretton

The reason I'm asking is that I've started using the following approach when it comes to debugging:

Code:

---

#ifdef DEBUG
printf("Test print: foo");
#endif

---

---

Consider doing something like this (if your print function is always simple like in your example).

Code:

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#ifndef NDEBUG
#define TRACE(x) puts(x)
#else
#define TRACE(x)
#endif

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Populate your function(s).

Code:

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int foo(int i)
{
  TRACE("foo");
  return i;
}

---