Initializing a 2D std::array using multiple std::arrays

Question

I am attempting to initialize a 2D std::array using arrays in C++:

const array<bool, 7> LEDZERO = { 1,1,1,0,1,1,1 };
const array<bool, 7> LEDONE[] = { 0,0,1,0,0,1,0 };
const array<bool, 7> LEDTWO[] = { 1,0,1,1,1,0,1 };
const array<bool, 7> LEDTHREE[] = { 1,0,1,1,0,1,1 };
const array<bool, 7> LEDFOUR[] = { 0,1,1,1,0,1,0 };
const array<bool, 7> LEDFIVE[] = { 1,1,0,1,0,1,1 };
const array<bool, 7> LEDSIX[] = { 1,1,0,1,1,1,1 };
const array<bool, 7> LEDSEVEN[] = { 1,0,1,0,0,1,0 };
const array<bool, 7> LEDEIGHT[] = { 1,1,1,1,1,1,1 };
const array<bool, 7> LEDNINE[] = { 1,1,1,1,0,1,0 };
const array<array<bool, 7>, 10> LEDS = { { {LEDZERO}, {LEDONE}, {LEDTWO},     
{LEDTHREE}, {LEDFOUR}, {LEDFIVE}, {LEDSIX}, {LEDSEVEN}, {LEDEIGHT}, 
{LEDNINE} } };

Only the first LEDZERO seems to be set to LEDS[0] correctly, LEDS[1-9] are wrong.

const array<bool, 7> LEDONE[] = { 0,0,1,0,0,1,0 }; -- See anything wrong with using []? The strange thing is that you didn't make the mistake with LEDZERO. — PaulMcKenzie
– PaulMcKenzie, Commented Dec 13, 2017 at 3:38
Oh I see, I had been trying to work with c-style arrays for a few hours and switched over to std::array. After some sleep I can see how obvious my mistake was! — Darkstorm51
– Darkstorm51, Commented Dec 13, 2017 at 15:03

Henri Menke · Accepted Answer · 2017-12-13 03:38:43Z

You have spurious [] after most LED variables. This will create a C-style array of std::array (probably not what you want).

#include <array>

int main()
{
    const std::array<bool, 7> LEDZERO = {{ 1,1,1,0,1,1,1 }};
    const std::array<bool, 7> LEDONE = {{ 0,0,1,0,0,1,0 }};
    const std::array<bool, 7> LEDTWO = {{ 1,0,1,1,1,0,1 }};
    const std::array<bool, 7> LEDTHREE = {{ 1,0,1,1,0,1,1 }};
    const std::array<bool, 7> LEDFOUR = {{ 0,1,1,1,0,1,0 }};
    const std::array<bool, 7> LEDFIVE = {{ 1,1,0,1,0,1,1 }};
    const std::array<bool, 7> LEDSIX = {{ 1,1,0,1,1,1,1 }};
    const std::array<bool, 7> LEDSEVEN = {{ 1,0,1,0,0,1,0 }};
    const std::array<bool, 7> LEDEIGHT = {{ 1,1,1,1,1,1,1 }};
    const std::array<bool, 7> LEDNINE = {{ 1,1,1,1,0,1,0 }};
    const std::array<std::array<bool, 7>, 10> LEDS = {{
            {LEDZERO},
            {LEDONE},
            {LEDTWO},     
            {LEDTHREE},
            {LEDFOUR},
            {LEDFIVE},
            {LEDSIX},
            {LEDSEVEN},
            {LEDEIGHT}, 
            {LEDNINE}
        }};
}

If you do not need LEDZERO through LEDNINE, you could write it more compact.

#include <array>

int main()
{
    const std::array<std::array<bool, 7>, 10> LEDS = {{
            {{ 1,1,1,0,1,1,1 }},
            {{ 0,0,1,0,0,1,0 }},
            {{ 1,0,1,1,1,0,1 }},
            {{ 1,0,1,1,0,1,1 }},
            {{ 0,1,1,1,0,1,0 }},
            {{ 1,1,0,1,0,1,1 }},
            {{ 1,1,0,1,1,1,1 }},
            {{ 1,0,1,0,0,1,0 }},
            {{ 1,1,1,1,1,1,1 }},
            {{ 1,1,1,1,0,1,0 }}
        }};
}

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