c标准里面只定义了int的最小宽度，所以这个范围就完全依赖于编译器的实现了。
请看c99的 5.2.4.2.1
Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown, with the same sign.
minimum value for an object of type int
INT_MIN -32767 // -(2^15 - 1)
