namespace std 定义的位置
其定义在yvals.h当中. 目录为Microsoft Visual Studio\VC98\INCLUDE
/* NAMESPACE */
#if defined(__cplusplus)
#define _STD_BEGIN namespace std {
#define _STD_END }
#define _STD ::std::
/*
We use the stdext (standard extension) namespace to contain extensions that are not part of the current standard
*/
#define _STDEXT_BEGIN namespace stdext {
#define _STDEXT_END }
#define _STDEXT ::stdext::
#ifdef _STD_USING
#define _C_STD_BEGIN namespace std { /* only if *.c compiled as C++ */
#define _C_STD_END }
#define _CSTD ::std::
#else /* _STD_USING */
/* #define _GLOBAL_USING *.h in global namespace, c* imports to std */
#define _C_STD_BEGIN
#define _C_STD_END
#define _CSTD ::
#endif /* _STD_USING */
#define _C_LIB_DECL extern "C " { /* C has extern "C " linkage */
#define _END_C_LIB_DECL }
#define _EXTERN_C extern "C " {
#define _END_EXTERN_C }
#else /* __cplusplus */
#define _STD_BEGIN
#define _STD_END
#define _STD
#define _C_STD_BEGIN
#define _C_STD_END
#define _CSTD
#define _C_LIB_DECL
#define _END_C_LIB_DECL
#define _EXTERN_C
#define _END_EXTERN_C
#endif /* __cplusplus */