# std::atan

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
float atan( float arg ); | (1) |
double atan( double arg ); | (2) |
long double atan( long double arg ); | (3) |
double atan( Integral arg ); | (4) | (since C++11)

Computes the principal value of the arc tangent of `arg`

4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).

### Parameters

arg | - | value of a floating-point or Integral type

### Return value

If no errors occur, the arc tangent of `arg` (arctan(arg)) in the range [-

π
2

; +

π
2

] radians, is returned.

If a range error occurs due to underflow, the correct result (after rounding) is returned.

### Error handling

Errors are reported as specified in math_errhandling

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

- If the argument is ±0, it is returned unmodified
- If the argument is +∞, +π/2 is returned
- If the argument is -∞, -π/2 is returned
- if the argument is NaN, NaN is returned

### Notes

POSIX specifies that in case of underflow, `arg` is returned unmodified, and if that is not supported, and implementation-defined value no greater than DBL_MIN, FLT_MIN, and LDBL_MIN is returned.

### Examples

Run this code

    #include <iostream>
    #include <cmath>

    int main()
    {
        std::cout << "atan(1) = " << atan(1) << " 4*atan(1) = " << 4*atan(1) << '\n';
        // special values
        std::cout << "atan(Inf) = " << atan(INFINITY)
                  << " 2*atan(Inf) = " << 2*atan(INFINITY) << '\n'
                  << "atan(-0.0) = " << atan(-0.0) << '\n'
                  << "atan(+0.0) = " << atan(0) << '\n';
    }

Output:

    atan(1) = 0.785398 4*atan(1) = 3.14159
    atan(Inf) = 1.5708 2*atan(Inf) = 3.14159
    atan(-0.0) = -0
    atan(+0.0) = 0

### See also

asin | computes arc sine (arcsin(x)) (function)
acos | computes arc cosine (arccos(x)) (function)
atan2 | arc tangent, using signs to determine quadrants (function)
tan | computes tangent (tan(x)) (function)
atan(std::complex) (C++11) | computes arc tangent of a complex number (arctan(z)) (function template)
atan(std::valarray) | applies the function std::atan to each element of valarray (function template)
C documentation for atan

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