Question

Are there extensions for C++ like there are in C#?

For example in C# you can do:

public static uint SwapEndian(this uint value)
{
    var tmp = BitConverter.GetBytes(value);
    Array.Reverse(tmp);
    return BitConverter.ToUInt32(tmp, 0);
}

someuint.SwapEndian();

Is there anything like that in C++?

Answer 1

Extension methods (and also “static classes”) exist in C#/Java languages solely because the designers decided that (the Java way of) OOP is The One True Way and that everything must be a method from a class:

This is not C++ way of doing things. In C++ you have namespaces, free functions and Koenig lookup to extend the behavior of a class:

namespace foo
{
    struct bar { ... };

    void act_on_bar(const bar& b) { ... };
}

...

foo::bar b;
act_on_bar(b); // No need to qualify because of Koenig lookup

I usually consider extension methods harmful. If you attach too much behavior to a class, you are proabably failing to capture the reason why the class exists. Also (like “partial classes”), they tend to make the code related to a class non local. Which is bad.

As to your problem, in C++ you simply do:

template <typename T>
T swap_endian(T x)
{
    union { T value; char bytes[sizeof(T)]; } u;
    u.value = x;

    for (size_t i = 0; i < sizeof(T)/2; i++) 
        swap(u.bytes[i], u.bytes[sizeof(T) - i - 1]);

    return u.value;
}

Usage:

swap_endian<std::uint32_t>(42);

or, if the type can be deduced:

std::uint64_t x = 42;
std::uint64_t y = swap_endian(x);