Conversion specifier of long double in C

Question

The long double data type can have these conversion specifiers in C: %Le,%LE,%Lf,%Lg,%LG (reference).

I wrote a small program to test :

#include <stdio.h>
int main(void) {
  long double d = 656546.67894L;
  printf("%.0Le\n",d);
  printf("%.0LE\n",d);
  printf("%.0Lf\n",d);
  printf("%.0Lg\n",d);
  printf("%.0LG\n",d);
  return 0; 
}

Output:

-0

-4E-153

-0

-4e-153

-4E-153

But none is giving the desired output, which is 656547 (as you may easily understand). What is the reason?

The compiler used is gcc version 3.4.2 (mingw-special).

Answer 1

From an old mingw wiki:

mingw uses the Microsoft C run-time libraries and their implementation of printf does not support the 'long double' type. As a work-around, you could cast to 'double' and pass that to printf instead. For example:

printf("value = %g\n", (double) my_long_double_value);

Note that a similar problem exists for 'long long' type. Use the 'I64' (eye sixty-four) length modifier instead of gcc's 'll' (ell ell). For example:

printf("value = %I64d\n", my_long_long_value);

Edit (6 years later): Also see the comment below from Keith Thompson for a workaround:

#define __USE_MINGW_ANSI_STDIO 1 in the source file or change the command line to gcc -D__USE_MINGW_ANSI_STDIO=1

Answer 2

The MinGW C library is provided by MSVCRT.DLL, which is shipped with Windows and is in fact the old VC++ 6.0 library.

MinGW does however use the GNU C++ library, and although that relies on the underlying C library, it does support long double for output using iostreams. Even if you do not wish to use C++ generally, it may be worth using just enough to support this capability.

Answer 3

using MinGW-W64 with architecture i686(x86-64 can't work) maybe a solution. I try it and it works.

These are compile info:

||=== Build: Debug in TeaErr (compiler: GNU GCC Compiler) ===|
D:\Practice\TeaErr\main.c||In function 'main':|
D:\Practice\TeaErr\main.c|7|warning: unknown conversion type character 'L' in format [-Wformat=]|
D:\Practice\TeaErr\main.c|7|warning: too many arguments for format [-Wformat-extra-args]|
D:\Practice\TeaErr\main.c|7|warning: unknown conversion type character 'L' in format [-Wformat=]|
D:\Practice\TeaErr\main.c|7|warning: too many arguments for format [-Wformat-extra-args]|
D:\Practice\TeaErr\main.c|8|warning: unknown conversion type character 'L' in format [-Wformat=]|
D:\Practice\TeaErr\main.c|8|warning: too many arguments for format [-Wformat-extra-args]|
D:\Practice\TeaErr\main.c|8|warning: unknown conversion type character 'L' in format [-Wformat=]|
D:\Practice\TeaErr\main.c|8|warning: too many arguments for format [-Wformat-extra-args]|
||=== Build finished: 0 error(s), 8 warning(s) (0 minute(s), 1 second(s)) ===|

These are my code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    long double a;
    scanf("%Lf",&a);
    printf("%Lf\n",a);
    return 0;
}

Result Some Parameters on Install MinGW-W64