linux编程中__THROW的含义

很多函数声明之后都会追加__THROW关键字。
找到源码，看看它到底是个啥东西：
(include/sys/cdefs.h)

/* GCC can always grok prototypes.  For C++ programs we add throw()
   to help it optimize the function calls.  But this works only with
   gcc 2.8.x and egcs.  For gcc 3.2 and up we even mark C functions
   as non-throwing using a function attribute since programs can use
   the -fexceptions options for C code as well.  */
# if !defined __cplusplus && __GNUC_PREREQ (3, 3)
#  define __THROW        __attribute__ ((__nothrow__ __LEAF))
#  define __THROWNL        __attribute__ ((__nothrow__))
#  define __NTH(fct)        __attribute__ ((__nothrow__ __LEAF)) fct
# else
#  if defined __cplusplus && __GNUC_PREREQ (2,8)
#   define __THROW        throw ()
#   define __THROWNL        throw ()
#   define __NTH(fct)        __LEAF_ATTR fct throw ()
#  else
#   define __THROW
#   define __THROWNL
#   define __NTH(fct)        fct
#  endif
# endif

从这里可以清楚的看到，当使用的是C语言的时候，__THROW不产生任何作用；当使用的是C++时，被__THROW修饰的函数将支持C++抛出异常的功能。