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在头文件<math.h>中定义



float       atanf( float arg );

(1)

(since C99)

double      atan( double arg );

(2)


long double atanl( long double arg );

(3)

(since C99)

Defined in header <tgmath.h>



#define atan( arg )

(4)

(since C99)

1-3）计算的反正切值的主值arg。

4）类型 - 通用宏：如果参数具有类型long double，atanl则被调用。否则，如果参数具有整数类型或类型double，atan则调用该参数。否则，atanf被调用。如果参数是复杂的，则宏调用相应的复变函数（catanf，catan，catanl）。

参数

arg

-

浮点值

返回值

如果没有错误发生，则arg（arctan（arg））的反正切值在[ -

| π |

|:----|

| 2 |

; +

| π |

|:----|

| 2 |

]弧度，返回。

如果由于下溢而发生范围错误，则返回正确的结果（舍入后）。

错误处理

按照math_errhandling中的指定报告错误。

如果实现支持IEEE浮点运算（IEC 60559），

  • 如果参数为±0，则不加修改地返回

  • 如果参数是+∞，则返回+π/ 2

  • 如果参数是-∞，则返回-π/ 2

  • 如果参数是NaN，则返回NaN

笔记

POSIX指定在发生下溢时，arg未经修改就返回，如果不支持，则返回不大于DBL_MIN，FLT_MIN和LDBL_MIN的实现定义值。

例

#include <stdio.h>#include <math.h>
 int main(void){    printf("atan(1) = %f, 4*atan(1)=%f\n", atan(1), 4*atan(1));    // special values    printf("atan(Inf) = %f, 2*atan(Inf) = %f\n", atan(INFINITY), 2*atan(INFINITY));    printf("atan(-0.0) = %+f, atan(+0.0) = %+f\n", atan(-0.0), atan(0));}

输出：

atan(1) = 0.785398, 4*atan(1)=3.141593atan(Inf) = 1.570796, 2*atan(Inf) = 3.141593atan(-0.0) = -0.000000, atan(+0.0) = +0.000000

参考

  • C11标准（ISO / IEC 9899：2011）：

    • 7.12.4.3 atan函数（p：238-239）

    • 7.25类型通用数学<tgmath.h>（p：373-375）

    • F.10.1.3 atan函数（p：519）

  • C99标准（ISO / IEC 9899：1999）：

    • 7.12.4.3 atan函数（p：219）

    • 7.22类型通用数学<tgmath.h>（p：335-337）

    • F.9.1.3 atan函数（p：456）

  • C89 / C90标准（ISO / IEC 9899：1990）：

    • 4.5.2.3 atan函数

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