std::tan, std::tanf, std::tanl

Defined in header <cmath>
float       tan ( float arg );
float       tanf( float arg );
(since C++11)
double      tan ( double arg );
long double tan ( long double arg );
long double tanl( long double arg );
(since C++11)
double      tan ( IntegralType arg );
(4) (since C++11)
1-3) Computes the tangent of arg (measured in radians).
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).


arg - value representing angle in radians, of a floating-point or Integral type

Return value

If no errors occur, the tangent of arg (tan(arg)) is returned.

The result may have little or no significance if the magnitude of arg is large.

(until C++11)

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

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 ±∞, NaN is returned and FE_INVALID is raised
  • if the argument is NaN, NaN is returned


The case where the argument is infinite is not specified to be a domain error in C (to which C++ defers), but it is defined as a domain error in POSIX.

The function has mathematical poles at π(1/2 + n); however no common floating-point representation is able to represent π/2 exactly, thus there is no value of the argument for which a pole error occurs.


#include <iostream>
#include <cmath>
#include <cerrno>
#include <cfenv>
const double pi = std::acos(-1); // or C++20's std::numbers::pi
int main()
    // typical usage
    std::cout << "tan(1*pi/4) = " << std::tan(1*pi/4) << '\n' // 45°
              << "tan(3*pi/4) = " << std::tan(3*pi/4) << '\n' // 135°
              << "tan(5*pi/4) = " << std::tan(5*pi/4) << '\n' // -135°
              << "tan(7*pi/4) = " << std::tan(7*pi/4) << '\n'; // -45°
    // special values
    std::cout << "tan(+0) = " << std::tan(0.0) << '\n'
              << "tan(-0) = " << std::tan(-0.0) << '\n';
    // error handling
    std::cout << "tan(INFINITY) = " << std::tan(INFINITY) << '\n';
    if (std::fetestexcept(FE_INVALID))
        std::cout << "    FE_INVALID raised\n";

Possible output:

tan(1*pi/4) = 1
tan(3*pi/4) = -1
tan(5*pi/4) = 1
tan(7*pi/4) = -1
tan(+0) = 0
tan(-0) = -0
tan(INFINITY) = -nan
    FE_INVALID raised

See also

computes sine (\({\small\sin{x} }\)sin(x))
computes cosine (\({\small\cos{x} }\)cos(x))
computes arc tangent (\({\small\arctan{x} }\)arctan(x))
computes tangent of a complex number (\({\small\tan{z} }\)tan(z))
(function template)
applies the function std::tan to each element of valarray
(function template)
C documentation for tan

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