L__FILE__ doesn't work...

This is a discussion on L__FILE__ doesn't work... within the C++ Programming forums, part of the General Programming Boards category; Hi, I'm wondering how the L macro (or whatever it is) works? It works fine with text in quotes like: ...

  1. #1
    and the hat of sweating
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    L__FILE__ doesn't work...

    Hi,
    I'm wondering how the L macro (or whatever it is) works?
    It works fine with text in quotes like: L"Hello world", but if I want to apply it to another macro like this: L__FILE__ the compiler can't figure out what I'm trying to do.
    I can get it to work using: _T( __FILE__ ), but that's a little ugly and non-standard.
    I tried: L( __FILE__ ), but then the compiler doesn't know what L is...
    Is there a way to make it work with L?

  2. #2
    Ex scientia vera
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    I just did a quick google, and I found that the L macro is for making string literals into unicode.

    How do you logically justify prefixing __FILE__ with the L macro?

    What is that supposed to do?

  3. #3
    and the hat of sweating
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    Quote Originally Posted by IceDane View Post
    I just did a quick google, and I found that the L macro is for making string literals into unicode.

    How do you logically justify prefixing __FILE__ with the L macro?

    What is that supposed to do?
    __FILE__ is an ASCII string, but I'm passing it to a function that takes UNICODE strings, so I need something like the L or _T() macro to do it...

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    L isn't a macro, it's a grammatical prefix (just like 1.0f -- the f isn't a macro), so it can only appear before a string literal. There may be a way to do some preprocessor trickery here, but I'm not seeing anything good off the top of my head.

  5. #5
    Just Lurking Dave_Sinkula's Avatar
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    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  6. #6
    Captain Crash brewbuck's Avatar
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    Why not just put a space:

    Code:
    L __FILE__
    Or does that not work?

  7. #7
    and the Hat of Guessing tabstop's Avatar
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    The preprocessor will recognize __FILE__ now, but you can't have a space between L and "xyz" to have a long string.

  8. #8
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by tabstop View Post
    The preprocessor will recognize __FILE__ now, but you can't have a space between L and "xyz" to have a long string.
    So then why not a macro:

    Code:
    #define MY_L(x) L##x
    That would allow for the two-stage expansion of __FILE__ to "blah.c" and then L##"blah.c" --> L"blah.c"

    EDIT: Doh, that's basically what Dave posted a link to (except the linked way actually works )
    Last edited by brewbuck; 04-07-2008 at 10:26 AM.

  9. #9
    and the hat of sweating
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    Quote Originally Posted by Dave_Sinkula View Post
    So I need 2 macros... strange. OK thanks.

  10. #10
    Kernel hacker
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    Yes, the first macro serves to "resolve" __FILE__ into "blah.c" or such, then the second does L + "blah.c".

    It's a "classic" trick.

    --
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