nRF24L01 pipe addresses and multi-dimensional arrays

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1

This is a rather fundamental question which I should not be grappling with but somehow am getting confused. And, since the code (which I am asking this question about) is from an example sketch (MulticeiverDemo.ino from the RF24 library by TMRh20) it surely can't be wrong.

Here's my confusion:

The pipe addresses are defined in a multi-dimensional array as below:

uint8_t address[6][5] = { { 0x78, 0x78, 0x78, 0x78, 0x78 },
                          { 0xF1, 0xB6, 0xB5, 0xB4, 0xB3 },
                          { 0xCD, 0xB6, 0xB5, 0xB4, 0xB3 },
                          { 0xA3, 0xB6, 0xB5, 0xB4, 0xB3 },
                          { 0x0F, 0xB6, 0xB5, 0xB4, 0xB3 },
                          { 0x05, 0xB6, 0xB5, 0xB4, 0xB3 } };

Then the pipes are opened for reading in a loop like so:

    for (uint8_t i = 0; i < 6; ++i)
      radio.openReadingPipe(i, address[i]);

Given that the second parameter should be of type uint8_t, and address[i] should give an array of values, how does this work?

2

No, this is incorrect.
Multidimension array is array of arrays, so every element of it is array itself. Array of uint8_t has a pointer type - uint8_t*, exactly as expected in openReadingPipe() method.

Did I answer the question?

3

it's a 2D array, address[i] is an array of five uint8_t, and in C/C++, when an array is passed to a function, it’s automatically converted to a pointer to its first element.

Here, when passed to radio.openReadingPipe(), in the body of the function, address[i] is implicitly treated as a uint8_t* pointing to address[i][0]

The doc only mentions a prototype being

void RF24::openReadingPipe(uint8_t number, uint64_t address);

so that seems bizarre that it would work but if you look at the source code you'll see there is a second API

void openReadingPipe(uint8_t number, const uint8_t* address);

that's why it works.

4

Oh, this totally clarifies. Thank you both @b707 and @J-M-L.