create and initialize a static const char array as Ascii Look up Table in c++

Question

Hey I tried to make a look up table to switch chars to upper case:

struct X {
    static const char lut[256];
};

int main(int argc, char** argv) {
    for(int i = 0; i < 256; i++) {
        char c = (char)i;
        if (c <= 'z' && c > 'Z') {
            X::lut[i]= (c-32);  
        }
        X::lut[i]=c;
    }
    return 0;
}

I know that this is the wrong way:( Can someone show me to do this correct?

Answer 1

You may use the following (in C++11):

#include <array>
#include <cctype>

std::array<char, 256> to_upper_array()
{
    std::array<char, 256> res;

    for (int i = 0; i != 256; ++i) {
        res[i] = char(std::toupper(i));
    }
    return res;
}

struct X {
    static const std::array<char, 256> lut;
};

const std::array<char, 256> X::lut = to_upper_array();