M_PI_2 报错

error C2065: “M_PI_2”: 未声明的标识符。

在Visual Studio中使用math.h库时与其他数学库冲突时，可以通过宏_USE_MATH_DEFINES来消除math.h定义的宏。

D:\Windows Kits\10\Include\10.0.20348.0\ucrt\corecrt_math_defines.h

//
// corecrt_math_defines.h
//
//      Copyright (c) Microsoft Corporation. All rights reserved.
//
// Definitions of useful mathematical constants
//
#pragma once
#ifndef _MATH_DEFINES_DEFINED
#define _MATH_DEFINES_DEFINED

#include 

#pragma warning(push)
#pragma warning(disable: _UCRT_DISABLED_WARNINGS)
_UCRT_DISABLE_CLANG_WARNINGS

// Definitions of useful mathematical constants
//
// Define _USE_MATH_DEFINES before including  to expose these macro
// definitions for common math constants.  These are placed under an #ifdef
// since these commonly-defined names are not part of the C or C++ standards
#define M_E        2.71828182845904523536   // e
#define M_LOG2E    1.44269504088896340736   // log2(e)
#define M_LOG10E   0.434294481903251827651  // log10(e)
#define M_LN2      0.693147180559945309417  // ln(2)
#define M_LN10     2.30258509299404568402   // ln(10)
#define M_PI       3.14159265358979323846   // pi
#define M_PI_2     1.57079632679489661923   // pi/2
#define M_PI_4     0.785398163397448309616  // pi/4
#define M_1_PI     0.318309886183790671538  // 1/pi
#define M_2_PI     0.636619772367581343076  // 2/pi
#define M_2_SQRTPI 1.12837916709551257390   // 2/sqrt(pi)
#define M_SQRT2    1.41421356237309504880   // sqrt(2)
#define M_SQRT1_2  0.707106781186547524401  // 1/sqrt(2)

_UCRT_RESTORE_CLANG_WARNINGS
#pragma warning(pop) // _UCRT_DISABLED_WARNINGS
#endif // _MATH_DEFINES_DEFINED

解决方法：