c 11模式中奇怪的g预处理器行为

$g++ --version
g++ (GCC) 4.7.2
Copyright (C) 2012 Free Software Foundation,Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

以下剪辑揭示了问题：

$cat foo.cpp
//#include <QtGui>
#define QTOSTRING_HELPER(s) #s
#define QTOSTRING(s) QTOSTRING_HELPER(s)
#ifndef QT_NO_DEBUG
# define QLOCATION ""__FILE__":"QTOSTRING(__LINE__)
# define METHOD(a)   qFlagLocation("0"#a QLOCATION)
# define SLOT(a)     qFlagLocation("1"#a QLOCATION)
# define SIGNAL(a)   qFlagLocation("2"#a QLOCATION)
#else
# define METHOD(a)   "0"#a
# define SLOT(a)     "1"#a
# define SIGNAL(a)   "2"#a
#endif

METHOD(grml)

在没有c 11的情况下对其进行预处理是正确的.

$g++ -E foo.cpp
# 1 "foo.cpp"
# 1 "<command-line>"
# 1 "foo.cpp"
# 15 "foo.cpp"
qFlagLocation("0""grml" """foo.cpp"":""15")

但是在C 11模式下,QTOSTRING宏不会扩展,导致源代码行出现编译错误.

$g++ -std=c++11 -E foo.cpp
# 1 "foo.cpp"
# 1 "<command-line>"
# 1 "foo.cpp"
# 15 "foo.cpp"
qFlagLocation("0""grml" ""__FILE__":"QTOSTRING(15))

这种行为是否有意,我该怎么做才能启用扩展？