上述代码在vc10.0和gcc上都能编译通过，输出ext。
这个问题，今天垒代码的时候第一次碰到~~~~当时很惊讶！！
翻了翻c++标准，参考了一下程序结果，大致知道了为什么。
ISO/IEC 14882:2003(E)/ 2.13.4 String literals/ P47:
A string literal is a sequence of characters (as defined in 2.13.2) surrounded by double quotes, optionally
beginning with the letter L, as in "..." or L"...". A string literal that does not begin with L is an ordinary
string literal, also referred to as a narrow string literal. An ordinary string literal has type “array of n
const char” and static storage duration (3.7), where n is the size of the string as defined below, and is
initialized with the given characters.
标准说的很明白，字符串字面值的类型 是一个const char数组的类型，"text"的类型是 const char[5],数组类型在进行算术运算时，
隐式进行一次Array-to-pointer conversion的标准转换，同时c++标准也明确指出了
ISO/IEC 14882:2003(E) /4.2 Array-to-pointer conversion/P88
A string literal (2.13.4) that is not a wide string literal can be converted to an rvalue of type “pointer to
char”; a wide string literal can be converted to an rvalue of type “pointer to wchar_t”. In either case,
the result is a pointer to the first element of the array. This conversion is considered only when there is an
explicit appropriate pointer target type, and not when there is a general need to convert from an lvalue to an
rvalue. [Note: this conversion is deprecated. See Annex D. ] For the purpose of ranking in overload resolution
(13.3.3.1.1), this conversion is considered an array-to-pointer conversion followed by a qualification
conversion (4.4). [Example: "abc" is converted to “pointer to const char” as an array-to-pointer conversion,
and then to “pointer to char” as a qualification conversion. ]
"text"在表达式中转换成一个char *，然后进行了一次算术运算，最终"text"+1 会返回一个const char *，指向了字符串常量的第2个字符的位置。
然后调用string的转型构造函数生成一个对象。