unsigned char array incompatible with pointer parameter

Question

I have this function

unsigned char NCN_System_upload(unsigned char *data, unsigned char len);

I have an array defined as such:

unsigned char data[3];

I'm using the function as the following:

NCN_System_upload(&data, 3);

However, I get the following error:

argument of type unsigned char (*)[3] is incompatible with parameter of type unsigned char*

Why doesn't this work?

Arrays naturally decays to pointers, so no need for the address-of operator. — Some programmer dude
– Some programmer dude, Commented Aug 22, 2015 at 13:59

BartoszKP · Accepted Answer · 2015-08-22 21:50:49Z

3

The name of the array is already (can be implicitly converted) to a pointer to its beginning. Thus, you should do it like this:

NCN_System_upload(data, 3);

edited Aug 22, 2015 at 21:50

answered Aug 22, 2015 at 13:57

BartoszKP

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3 Comments

user2741466 Over a year ago

I knew I was being super dumb. Thanks!

Serge Ballesta Over a year ago

The official wording would be the name of the array already decays to a pointer.... Arrays do not always act the same as pointers.

Peter Over a year ago

Actually, "decays" is an informal description as well (albeit one a lot of people seem to use). The description in the standard - bearing in mind that the purpose of the standard is to be the definitive specification - is that "An lvalue or rvalue of type “array of N T” or “array of unknown bound of T” can be converted to an rvalue of type “pointer to T.” The result is a pointer to the first element of the array." This is a long-winded way of describing an implicit conversion. The word "decay" (or variants) does not even appear in the standards.

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