如何将此C代码转换为C ++？

Question

I have some arrays that are declared like this:

static double covalent_radius[256] = {
    [ 0 ] = 0.85,
    [ 1 ] = 0.37,
    ...
};

C++ doesn't allow this kind of declaration. Is there any way to achieve this?

Answer 1

static double covalent_radius[256] = {
    0.85, /* ?,  Unknown    */
    0.37, /* H,  Hydrogen   */
    ...
};

It's C89, not C99 so I suppose it should work.

Answer 2

Why don't you do this:

static double covalent_radius[256] = {
    0.85, /* 0: ?,  Unknown    */
    0.37, /* 1: H,  Hydrogen   */
    ...
};

Answer 3

You could use a std::vector of a std::tuple of two std::string and a double

#include <iostream>
#include <string>
#include <tuple>
#include <vector>

static auto periodic_table = std::vector<std::tuple<std::string, std::string, double>> 
{
    std::make_tuple("?", "Unknown", 0.85),
    std::make_tuple("H", "Hydrogen", 0.37)
};

std::string element_symbol(int neutrons)
{
    return std::get<0>(periodic_table[neutrons]);    
}

std::string element_name(int neutrons)
{
    return std::get<1>(periodic_table[neutrons]);    
}

double covalent_radius(int neutrons)
{
    return std::get<2>(periodic_table[neutrons]);    
}

int main() 
{
    std::cout << element_symbol(1) << "\n";
    std::cout << element_name(1) << "\n";
    std::cout << covalent_radius(1) << "\n";
}

Live Example (using C++11 initializer-lists).

Note : I'd make the periodic table std::vector instead of an array because they keep synthesizing new (unstable) elements.