"long double" and "printf"

Discussion in 'C Programming' started by Zero, Jun 6, 2006.

  1. Zero

    Zero Guest

    Hi everybody,

    i want to write a small program, which shows me the biggest and
    smallest number in dependance of the data type.

    For int the command could be:

    printf("\n%20s\t%7u\t%13i\t%13i","signed int",sizeof(signed
    int),INT_MIN,INT_MAX);

    But what do I have to do when I want to print out the numbers of data
    type "long double".

    I tried
    printf("\n%20s\t%7u\t%13Lf\t%13Lf","long double",sizeof(long
    double),LDBL_MIN,LDBL_MAX);
    but this results in

    long double 12 0.000000 -1.#QNAN0

    Does anybody has a solution.

    I tried this with Bloodshed using the gnu-compiler.

    Thanks for your help!
     
    Zero, Jun 6, 2006
    #1
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  2. Zero

    pete Guest

    For something like that,
    you should try to post a complete program.

    /* BEGIN new.c */

    #include <stdio.h>
    #include <float.h>

    int main(void)
    {
    printf("%s\n%u\n%Le\n%Le\n",
    "long double",
    (unsigned)sizeof(long double),
    LDBL_MIN,
    LDBL_MAX);
    return 0;
    }

    /* END new.c */
     
    pete, Jun 6, 2006
    #2
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  3. Zero

    Zero Guest

    Thanks for your help. But i still get this message:

    long double
    12
    0.000000e+000
    -1.#QNAN0e+000

    ??
     
    Zero, Jun 6, 2006
    #3
  4. Zero

    Richard Bos Guest

    AFAICT this is a bug in Dev-C++. Their library and their headers don't
    match on this detail. One (IIRC the header) thinks long doubles are
    larger than doubles, the other (IIRC the printf() code) thinks they're
    as large as doubles.

    Richard
     
    Richard Bos, Jun 6, 2006
    #4
  5. Some older compilers did use 'll' in stead of 'L' for long double.
     
    Dik T. Winter, Jun 6, 2006
    #5
  6. Zero

    Zero Guest

    I just tried the code with Visual C++ and there it seems
    that there is no difference between double and long double?

    Bloodshed says long double consists of 12 Bytes, Visual C++ says 12.
    What is right now?
     
    Zero, Jun 6, 2006
    #6
  7. Zero

    Zero Guest

    I just tried the code with Visual C++ and there it seems
    that there is no difference between double and long double?

    Bloodshed says long double consists of 12 Bytes, Visual C++ says 8.
    What is right now?
     
    Zero, Jun 6, 2006
    #7
  8. Zero

    Zero Guest

    How do you know that this is a bug? Is there a side, where this
    information can be fetched?
     
    Zero, Jun 6, 2006
    #8
  9. Zero

    Flash Gordon Guest

    Zero wrote:

    Both. The C standard does not mandate exact sizes only minimums.
     
    Flash Gordon, Jun 6, 2006
    #9
  10. Zero

    Tim Prince Guest

    Besides, the amount of unused storage doesn't directly answer your
    problem. Few of us would know whether specifying Bloodshed implies a
    specific version of gcc and run-time library. Run-time libraries
    associated with Windows versions of gcc which I have used didn't
    implement 10-byte long double in printf(), even though it might be
    supported in terms of basic operators. If it uses Visual C++ printf(),
    evidently there will be no support for more than 8-byte data type.
     
    Tim Prince, Jun 6, 2006
    #10
  11. Zero

    Dann Corbit Guest

    I guess that he is using the GCC MINGW compiler which creates 80 bit
    hardware long doubles, but which the Microsoft runtime libraries do not
    match (for MS VC++ double and long double are the same type).
     
    Dann Corbit, Jun 6, 2006
    #11
  12. Zero

    jacob navia Guest

    pete a écrit :

    This produces:
    long double
    12
    3.362103e-4932
    1.189731e+4932

    with lcc-win32
     
    jacob navia, Jun 6, 2006
    #12
  13. Zero

    Richard Bos Guest

    For starters, because the behaviour you observe is not correct. There
    was a c.l.c thread on this very problem some time ago; if you search for
    it I'm sure you can find it. In that thread, some people (including me)
    did some experiments and concluded that it had to be a mismatch
    somewhere in Dev-C++.

    Richard
     
    Richard Bos, Jun 8, 2006
    #13
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