[Bug c/46908] New: printf not handling printing of double correctly in certain cases

[Bug c/46908] New: printf not handling printing of double correctly in certain cases

[adrian.hawryluk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

           Summary: printf not handling printing of double correctly in
                    certain cases
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: adrian.hawryluk@gmail.com
              Host: Windows XP SP2
            Target: mingw32
             Build: 4.5.0


This is a weird one.  Under different compile options, it does it wrong in
different ways. :)

#include <stdio.h>
#include <math.h>
void printld(long double* pld)
{
    int i;
    printf("*%p = ", pld);
    for (i = 0; i < sizeof(long double); ++i) {
        printf("%02x ", ((unsigned char*)pld)[i]);
    }
    printf("\n");
}

int main()
{
    long double number1 = 1.0;
    long double number2 = 1.0;

    printf ("%lf, %lf\n", number1, number2);

    printf ("Enter number1: ");
    scanf ("%lf", &number1);
    printf ("Enter number2: ");
    scanf ("%lf", &number2);

    printf ("%lf, %lf\n", number1, number2);
    printf ("%lf, %lf\n", number1, number1);

    printld(&number1);
    printld(&number2);
    return 0;
}

C:\tmp>gcc -o tmp.exe file.c

C:\tmp>tmp
0.000000, 0.000000
Enter number1: 3
Enter number2: 4
3.000000, 0.000000
3.000000, 0.000000
*0022FF30 = 00 00 00 00 00 00 08 40 ff 3f 00 00
*0022FF20 = 00 00 00 00 00 00 10 40 ff 3f 00 00

C:\tmp>gcc -std=c99 -o tmp.exe file.c

C:\tmp>tmp
1.000000, 1.000000
Enter number1: 3
Enter number2: 4
0.000000, 0.000000
0.000000, 0.000000
*0022ff30 = 00 00 00 00 00 00 08 40 ff 3f 00 00
*0022ff20 = 00 00 00 00 00 00 10 40 ff 3f 00 00

There was even a way of printing the same variable (number1) twice on a line
and it would output it twice.  That is why I had put in:

  printf ("%lf, %lf\n", number1, number1);

as a test, but it didn't show up in this test code.

C:\tmp>gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=c:/mingw/bin/../libexec/gcc/mingw32/4.5.0/lto-wrapper.exe
Target: mingw32
Configured with: ../gcc-4.5.0/configure
--enable-languages=c,c++,ada,fortran,objc,obj-c++ --disable-sjlj-exceptions
--with-dwarf2 --enable-shared --enable-libgomp --disable-win32-registry
--enable-libstdcxx-debug --enable-version-specific-runtime-libs
--disable-werror --build=mingw32 --prefix=/mingw

Thread model: win32
gcc version 4.5.0 (GCC)
--
A

[Bug c/46908] printf not handling printing of double correctly in certain cases

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> 2010-12-12 16:51:28 UTC ---
l has no effect on %f.

[Bug c/46908] printf not handling printing of double correctly in certain cases

[manu at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu.org

--- Comment #2 from Manuel López-Ibáñez <manu at gcc dot gnu.org> 2010-12-12 17:32:26 UTC ---
Use -Wall:

test.c:18: warning: format ‘%f’ expects type ‘double’, but argument 2 has type
‘long double’

which means that %f is not for long double, you should use %Lf and it will
work.

[Bug c/46908] printf not handling printing of double correctly in certain cases

[adrian.hawryluk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

Adrian Hawryluk <adrian.hawryluk at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |

--- Comment #3 from Adrian Hawryluk <adrian.hawryluk at gmail dot com> 2010-12-12 22:53:43 UTC ---
Sorry, changed to %Lf with same results.   

#include <stdio.h>
#include <math.h>
void printld(long double* pld)
{
    int i;
    printf("*%p = ", pld);
    for (i = 0; i < sizeof(long double); ++i) {
        printf("%02x ", ((unsigned char*)pld)[i]);
    }
    printf("\n");
}

int main()
{
    long double number1 = 1.0;
    long double number2 = 1.0;

    printf ("%Lf, %Lf\n", number1, number2);

    printf ("Enter number1: ");
    scanf (" %Lf", &number1);
    printf ("Enter number2: ");
    scanf (" %Lf", &number2);

    printf ("%Lf, %Lf\n", number1, number2);
    printf ("%Lf, %Lf\n", number1, number1);

    printld(&number1);
    printld(&number2);
    return 0;
}

[Bug c/46908] printf not handling printing of double correctly in certain cases

[adrian.hawryluk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

--- Comment #4 from Adrian Hawryluk <adrian.hawryluk at gmail dot com> 2010-12-12 22:55:47 UTC ---
But found that "L" is not a known conversion type character.  When is "L"
supposed to be implemented?

C:\tmp>gcc -Wall -o tmp.exe file.c
file.c: In function 'main':
file.c:18:5: warning: unknown conversion type character 'L' in format
file.c:18:5: warning: unknown conversion type character 'L' in format
file.c:18:5: warning: too many arguments for format
file.c:21:5: warning: unknown conversion type character 'L' in format
file.c:21:5: warning: too many arguments for format
file.c:23:5: warning: unknown conversion type character 'L' in format
file.c:23:5: warning: too many arguments for format
file.c:25:5: warning: unknown conversion type character 'L' in format
file.c:25:5: warning: unknown conversion type character 'L' in format
file.c:25:5: warning: too many arguments for format
file.c:26:5: warning: unknown conversion type character 'L' in format
file.c:26:5: warning: unknown conversion type character 'L' in format
file.c:26:5: warning: too many arguments for format

[Bug c/46908] printf not handling printing of double correctly in certain cases

[adrian.hawryluk at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

--- Comment #5 from Adrian Hawryluk <adrian.hawryluk at gmail dot com> 2010-12-12 23:08:58 UTC ---
Used flag -std=c99 and this reduced the number of warnings.  They were limited
to the scanf format string.

C:\tmp>gcc -Wall -std=c99 -o tmp.exe file.c
file.c: In function 'main':
file.c:21:5: warning: unknown conversion type character 'L' in format
file.c:21:5: warning: too many arguments for format
file.c:23:5: warning: unknown conversion type character 'L' in format
file.c:23:5: warning: too many arguments for format

[Bug target/46908] printf not handling printing of double correctly in certain cases

[jsm28 at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46908

Joseph S. Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
          Component|c                           |target
         Resolution|                            |INVALID

--- Comment #6 from Joseph S. Myers <jsm28 at gcc dot gnu.org> 2010-12-13 18:28:22 UTC ---
GCC knows about the limitations of the Windows (msvcrt) printf and scanf
functions, which do not support all standard C99 formats, and the warnings are
telling you that they are not supported by those libraries.  The MinGW
libraries (wrapping msvcrt) are a separate project from GCC and there is no GCC
bug here.