atan-atanf-atanl-atan2-atan2f-atan2l.md

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atan, atanf, atanl, atan2, atan2f, atan2l | Microsoft Docs		11/04/2016			cpp-standard-libraries		article	atan2f atan2l atan2 atanf atan atanl	msvcrt.dll msvcr80.dll msvcr90.dll msvcr100.dll msvcr100_clr0400.dll msvcr110.dll msvcr110_clr0400.dll msvcr120.dll msvcr120_clr0400.dll ucrtbase.dll api-ms-win-crt-math-l1-1-0.dll	DLLExport	atan atan2l atan2 atanl atanf atan2f	C++	atan function atanf function atanl function atan2 function atan2l function arctangent function trigonometric functions atan2f function	7a87a18e-c94d-4727-9cb1-1bb5c2725ae4	21	corob-msft	corob	ghogen

atan, atanf, atanl, atan2, atan2f, atan2l

Calculates the arctangent of x (atan, atanf, and atanl) or the arctangent of y/x (atan2, atan2f, and atan2l).

Syntax

double atan(   
   double x   
);  
float atan(  
   float x   
);  // C++ only  
long double atan(  
   long double x  
);  // C++ only  
double atan2(   
   double y,   
   double x   
);  
float atan2(  
   float y,  
   float x  
);  // C++ only  
long double atan2(  
   long double y,  
   long double x  
);  // C++ only  
float atanf(   
   float x   
);  
long double atanl(  
   long double x  
);  
float atan2f(  
   float y,  
   float x  
);  
long double atan2l(  
   long double y,  
   long double x  
);  

Parameters

x, y
Any numbers.

Return Value

atan returns the arctangent of x in the range -π/2 to π/2 radians. atan2 returns the arctangent of y/x in the range -π to π radians. If x is 0, atan returns 0. If both parameters of atan2 are 0, the function returns 0. All results are in radians.

atan2 uses the signs of both parameters to determine the quadrant of the return value.

Input	SEH Exception	Matherr Exception
± QNAN,IND	none	_DOMAIN

Remarks

The atan function calculates the arctangent (the inverse tangent function) of x. atan2 calculates the arctangent of y/x (if x equals 0, atan2 returns π/2 if y is positive, -π/2 if y is negative, or 0 if y is 0.)

atan has an implementation that uses Streaming SIMD Extensions 2 (SSE2). For information and restrictions about using the SSE2 implementation, see _set_SSE2_enable.

Because C++ allows overloading, you can call overloads of atan and atan2. In a C program, atan and atan2 always take and return doubles.

Requirements

Routine	Required header
atan, atan2, atanf, atan2f, atanl, atan2l	<math.h>

Example

// crt_atan.c  
// arguments: 5 0.5  
#include <math.h>  
#include <stdio.h>  
#include <errno.h>  
  
int main( int ac, char* av[] )   
{  
   double x, y, theta;  
   if( ac != 3 ){  
      fprintf( stderr, "Usage: %s <x> <y>\n", av[0] );  
      return 1;  
   }  
   x = atof( av[1] );  
   theta = atan( x );  
   printf( "Arctangent of %f: %f\n", x, theta );  
   y = atof( av[2] );  
   theta = atan2( y, x );  
   printf( "Arctangent of %f / %f: %f\n", y, x, theta );   
   return 0;  
}  

Arctangent of 5.000000: 1.373401  
Arctangent of 0.500000 / 5.000000: 0.099669  

See Also

Floating-Point Support
acos, acosf, acosl
asin, asinf, asinl
cos, cosf, cosl, cosh, coshf, coshl
_matherr
sin, sinf, sinl, sinh, sinhf, sinhl
tan, tanf, tanl, tanh, tanhf, tanhl
_CIatan
_CIatan2