【错误】 y1重定义，以前的定义是“函数”

今天敲代码发现这个错误，找半天也没发现到底是哪里重定义了，
把错误列表往上拉了一下，才发现…

我是个憨憨，原来这个y1在math.h里定义过了。有点神奇，居然写了个这么常用的命名方式做它的函数名。

继续打开math.h - corecrt_math.h ，让我来看看到底是哪个神奇函数在作怪，
然后你会发现，不仅是y1,连j0,j1,jn,y0,yn都被定义了，

作用：

Function: double j0 (double x)
j0 returns the Bessel function of the first kind of order 0 of x. It may signal underflow if x is too large.

Function: double j1 (double x)
j1 returns the Bessel function of the first kind of order 1 of x. It may signal underflow if x is too large.

Function: double jn (int n, double x)
jn returns the Bessel function of the first kind of order n of x. It may signal underflow if x is too large.

Function: double y0 (double x)
y0 returns the Bessel function of the second kind of order 0 of x. It may signal underflow if x is too large. If x is negative, y0 signals a domain error; if it is zero, y0 signals overflow and returns -∞.

Function: double y1 (double x)y1 returns the Bessel function of the second kind of order 1 of x. It may signal underflow if x is too large. If x is negative, y1 signals a domain error; if it is zero, y1 signals overflow and returns -∞.

Function: double yn (int n, double x)yn returns the Bessel function of the second kind of order n of x. It may signal underflow if x is too large. If x is negative, yn signals a domain error; if it is zero, yn signals overflow and returns -∞.

大概意思就是返回一个贝塞尔函数什么什么的（没学过贝塞尔，不乱翻译了）

参考：

• Standard library header < math >
• These are some more exotic mathematical functions .