Merge multiple Arrays to one 2D Array

Question

I have this code snippet here:


#define byte uint8_t

byte pins0[11] = {  0,  1,  2, 3,   4,  5,  6,  7, 63, 64, 65};
byte pins1[11] = {  8,  9, 10, 11, 12, 13, 14, 15, 60, 61, 62};
byte pins2[11] = { 16, 17, 18, 19, 20, 21, 22, 15, 60, 61, 62};
byte pins3[11] = { 23, 24, 25, 26, 27, 28, 29, 30, 60, 61, 62};
byte pins4[11] = { 31, 32, 33, 34, 35, 36, 37, 38, 60, 61, 62};
byte pins5[11] = { 39, 40, 41, 42, 43, 44, 45, 46, 60, 61, 62};

byte *segPins[6] = {&pins0,&pins1,&pins2,&pins3,&pins4,&pins5};

The compiler shows an error:

src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
 byte *segPins[11] = {&pins0,&pins1,&pins2,&pins3,&pins4,&pins5};
                                                               ^
src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
src\main.cpp:15:63: error: cannot convert 'byte (*)[11] {aka unsigned char (*)[11]}' to 'byte* {aka unsigned char*}' in initialization
*** [.pio\build\nanoatmega328\src\main.cpp.o] Error 1

In my opinion, segPins is an Array of byte pointers. So it should pass the compiler but it sees a difference?

shouldn't segPins be an array of ptrs to an array of 11 bytes? — doug
– doug, Commented Nov 3, 2019 at 20:31
byte *segPins[6] = {pins0,pins1,...}; &pins0 is a address of the pointer which is pointing on array of 11 elements and can be bind to byte**ptr = &pins0. PS: Note I'm talking now about the case when array decay to pointer but u should understand general situation) — Roout
– Roout, Commented Nov 3, 2019 at 20:42
No. byte (*segPins[6])[11]; However, brj's answer is simpler and more typically how this should be done. — doug
– doug, Commented Nov 3, 2019 at 20:43
Why using the pre-processor? use type-alias is safer. using byte = uint8_t; or typedef. — Itachi Uchiwa
– Itachi Uchiwa, Commented Nov 3, 2019 at 21:00

brj · Accepted Answer · 2019-11-03 20:42:49Z

2

What you need is

byte *segPins[6] = {pins0,pins1,pins2,pins3,pins4,pins5};

This is because &pins0 refers to the address of the array pins0.

Edit

For more information see answers to this question.

edited Nov 3, 2019 at 20:42

answered Nov 3, 2019 at 20:37

brj

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