我用的IDE是Code::blocks，编译器是gcc

long double ld = 0.123L;
    printf("%Lf\n", ld);

运行上面一段代码后输出的是:

书上说的也是"%Lf"，但是这里为什么不行呢，网查了也是说用"%Lf"。

linux下正常

Windows下应该怎么办呢？

你用的mingw？

对。。

哎，刚刚试了下，确实不行，今天有事，明天再交流

谢谢你啊。。。

long double a;
cout << a << endl;

printf()里应该用什么格式字符串呢？？？

1) MinGW supports 80-bit long doubles; MSVC uses only 64-bits,
   (exactly the same as double).

2) MinGW uses Microsoft's MSVCRT runtime; the printf() routines
   in that can't interpret 80-bit long doubles.

In the majority of the references, turned up by the above links,
that is made abundantly clear; most suggest casting long double
to double, in the printf() call, so MSVCRT's printf() can format
the data, albeit with loss of precision.

The alternative, as most of the references state, is to wait for
some kind soul to provide an alternative printf() implementation,
which can interpret 80-bit long doubles.  What makes most of
those references obsolete is, that since mingwrt-3.15 was released,
that alternative implementation is available; however, the default
is still to use the MSVCRT implementation.  If you want to use the
alternative implementation, you have to request it; you do this
by adding `-ansi' or `-posix' to your compile options, or by adding
any of the related defines, as specified in _mingw.h.