# std::exp2, std::exp2f, std::exp2l

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
float exp2 ( float num ); double exp2 ( double num ); long double exp2 ( long double num ); |  | (until C++23)
/* floating-point-type */ exp2 ( /* floating-point-type */ num ); |  | (since C++23) (constexpr since C++26)
float exp2f( float num ); | (2) | (since C++11) (constexpr since C++26)
long double exp2l( long double num ); | (3) | (since C++11) (constexpr since C++26)
Additional overloads (since C++11) |  |
Defined in header `<cmath>` |  |
template< class Integer > double exp2 ( Integer num ); | (A) | (constexpr since C++26)

1-3) Computes 2 raised to the given power num. The library provides overloads of `std::exp2` for all cv-unqualified floating-point types as the type of the parameter. (since C++23)

A) Additional overloads are provided for all integer types, which are treated as double. | (since C++11)

### Parameters

num | - | floating-point or integer value

### Return value

If no errors occur, the base-2 exponential of num (2num
) is returned.

If a range error due to overflow occurs, +HUGE_VAL, `+HUGE_VALF`, or `+HUGE_VALL` 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, 1 is returned
- If the argument is -∞, +0 is returned
- If the argument is +∞, +∞ is returned
- If the argument is NaN, NaN is returned

### Notes

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::exp2(num) has the same effect as std::exp2(static_cast<double>(num)).

### Example

Run this code

    #include <cerrno>
    #include <cfenv>
    #include <cmath>
    #include <cstring>
    #include <iostream>

    // #pragma STDC FENV_ACCESS ON

    int main()
    {
        std::cout << "exp2(4) = " << std::exp2(4) << '\n'
                  << "exp2(0.5) = " << std::exp2(0.5) << '\n'
                  << "exp2(-4) = " << std::exp2(-4) << '\n';

        // special values
        std::cout << "exp2(-0) = " << std::exp2(-0.0) << '\n'
                  << "exp2(-Inf) = " << std::exp2(-INFINITY) << '\n';

        // error handling
        errno = 0;
        std::feclearexcept(FE_ALL_EXCEPT);

        std::cout << "exp2(1024) = " << std::exp2(1024) << '\n';

        if (errno == ERANGE)
            std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
        if (std::fetestexcept(FE_OVERFLOW))
            std::cout << "    FE_OVERFLOW raised\n";
    }

Possible output:

    exp2(4) = 16
    exp2(0.5) = 1.41421
    exp2(-4) = 0.0625
    exp2(-0) = 1
    exp2(-Inf) = 0
    exp2(1024) = inf
        errno == ERANGE: Numerical result out of range
        FE_OVERFLOW raised

### See also

exp expf expl (C++11)(C++11) | returns e raised to the given power (\({\small e^x}\)ex) (function)
expm1 expm1f expm1l (C++11)(C++11)(C++11) | returns e raised to the given power, minus one (\({\small e^x-1}\)ex-1) (function)
log2 log2f log2l (C++11)(C++11)(C++11) | base 2 logarithm of the given number (\({\small \log_{2}{x} }\)log2(x)) (function)

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