std::exp, std::expf, std::expl

Since C++26

Header: <cmath>

1-3) Computes e (Euler’s number, 2.7182818…) raised to the given power num.The library provides overloads of std::exp for all cv-unqualified floating-point types as the type of the parameter.(since C++23)

# Declarations

float exp ( float num );
double exp ( double num );
long double exp ( long double num );

(until C++23)

/*floating-point-type*/
exp ( /*floating-point-type*/ num );

(since C++23) (constexpr since C++26)

float expf( float num );

(since C++11) (constexpr since C++26)

long double expl( long double num );

(since C++11) (constexpr since C++26)

SIMD overload (since C++26)

template< /*math-floating-point*/ V >
constexpr /*deduced-simd-t*/<V>
exp ( const V& v_num );

(since C++26)

Additional overloads (since C++11)

template< class Integer >
double exp ( Integer num );

(constexpr since C++26)

# Parameters

# Return value

If no errors occur, the base-e exponential of num (enum) is returned.

# Notes

For IEEE-compatible type double, overflow is guaranteed if 709.8 < num, and underflow is guaranteed if num < -708.4.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::exp(num) has the same effect as std::exp(static_cast(num)).

# Example

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <numbers>
 
// #pragma STDC FENV_ACCESS ON
 
consteval double approx_e()
{
    long double e{1.0};
    for (auto fac{1ull}, n{1llu}; n != 18; ++n, fac *= n)
        e += 1.0 / fac;
    return e;
}
 
int main()
{
    std::cout << std::setprecision(16)
              << "exp(1) = e¹ = " << std::exp(1) << '\n'
              << "numbers::e  = " << std::numbers::e << '\n'
              << "approx_e    = " << approx_e() << '\n'
              << "FV of $100, continuously compounded at 3% for 1 year = "
              << std::setprecision(6) << 100 * std::exp(0.03) << '\n';
 
    // special values
    std::cout << "exp(-0) = " << std::exp(-0.0) << '\n'
              << "exp(-Inf) = " << std::exp(-INFINITY) << '\n';
 
    // error handling 
    errno = 0;
    std::feclearexcept(FE_ALL_EXCEPT);
 
    std::cout << "exp(710) = " << std::exp(710) << '\n';
 
    if (errno == ERANGE)
        std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
    if (std::fetestexcept(FE_OVERFLOW))
        std::cout << "    FE_OVERFLOW raised\n";
}

# See also