need a macro that does nothing

This is a discussion on need a macro that does nothing within the C Programming forums, part of the General Programming Boards category; I'm trying to write (and debug) a module for a library. All functions have to be statics so they don't ...

  1. #1
    not-a-geek
    Join Date
    Apr 2004
    Posts
    210

    need a macro that does nothing

    I'm trying to write (and debug) a module for a library. All functions have to be statics so they don't show up as one of the library's symbols. Unfortunatly this also prevents their names from showing up in any backtraces.
    Now I'm either looking for a simple way to switch between a debug compile where those functions are non-static and a build where they are marked static - or a way to make statics show up in my backtraces (glibc:backtrace()). I figured the former should be simple......

    For other debug functions I used the usual ((void)0) macros, so the obvious thing was to try something like...

    Code:
    #ifdef DEBUG
      #define _static ((void)0)
      [...]
    #else
      #define _static static
      [...]
    #endif
    (I named the macro "_static" instead of "static" because I don't want this to affect statics-in-a-function)

    As you might have already guessed, ((void)0) doesn't seem to be working for me in this case. I'm getting tons of errors like

    Code:
    client.c:3023: error: Syntaxfehler before "void"
    client.c:3024: error: Syntaxfehler before '(' token
    So the question would be how to make a macro that does exactly nothing, or how would I tell gcc not to strip names for static symbols (the manual didn't help me, btw).
    main() { int O[!0<<~-!0]; (!0<<!0)[O]+= ~0 +~(!0|!0<<!0); printf("a function calling "); }

  2. #2
    and the hat of int overfl Salem's Avatar
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    Read the manual page for the linker, and look up the options
    -S
    -s
    --retain-symbols-file

  3. #3
    Yes, my avatar is stolen anonytmouse's Avatar
    Join Date
    Dec 2002
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    2,544
    It's simpler than you think.
    Code:
    #define nothing
    On a side note, symbols with a leading underscore are typically reserved for use by the compiler.

  4. #4
    not-a-geek
    Join Date
    Apr 2004
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    210
    Ouch, thanks for directing me to the linker manual. I was searching the gcc manual...

    So, do I understand this right, you say I should remove all "static"s from the source and define only those symbols I want to retain instead? That sounds like a neat solution as there are only 2 functions that need to be accessible.

    I did that. nm -g (show external symbols) only lists the two symbols I listest in the symbols-retain-file, but nm -D (show dynamic symbols) now shows the ones I made non-static and I'm not sure if that is a problem or not. Is it now possible to link against those in the .so-file by accident?

    On a sidenote, I just realized I know next to nothing about linking. Google is my friend, but if anybody got some link (uhm, no pun...) to a really good document, I'd really like to know it
    Thanks for helping so far, Salem!

    edit: Thanks anonytmouse, I didn't see your post in time and will try that too, but Salem got me interested...
    edit2: Yup that really works.
    Last edited by Nyda; 11-18-2004 at 08:17 AM.
    main() { int O[!0<<~-!0]; (!0<<!0)[O]+= ~0 +~(!0|!0<<!0); printf("a function calling "); }

  5. #5
    Registered User
    Join Date
    Jun 2004
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    722
    Code:
    #ifdef DEBUG
      #define _static //_static does nothing
      [...]
    #else
      #define _static static //_static is static
      [...]
    #endif

  6. #6
    Gawking at stupidity
    Join Date
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    Be careful, _static might introde on your compiler's namespace. According to the C standard, if you want to be sure to avoid such conflicts you should use a trailing underscore instead (e.g. static_).
    If you understand what you're doing, you're not learning anything.

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