Reverse a string

Reverse.cpp

#include <cstdio>
#include <utility>

template <typename T, size_t N>
constexpr void Reverse(T (&str)[N])
{
    constexpr size_t len = N - 2;

    for (size_t i = 0, j = len; i <= j; ++i, --j)
        std::swap(str[i], str[j]);
}

template <typename T>
constexpr void ReverseNullTerminated(T* str)
{
    if (!str)
        return;

    T* left = &str[0];
    T* right = &str[0];

    while (right[1] != '\0')
        ++right;

    while (left != right)
    {
        std::swap(*left, *right);
        ++left;
        --right;
    }
}

int main(int argc, char** argv)
{
    if (argc < 2)
    {
        return -1;
    }

    char test[] = "Hello!";
    Reverse(test);
    puts(test);

    ReverseNullTerminated(argv[1]);
    puts(argv[1]);

    char* test2 = "";
    ReverseNullTerminated(test2);
    puts(test2);

    return 0;
}