C++ - Parentheses after variable name in declaration

Question

I'm looking at some Arduino code and encountering a construct I haven't seen before:

CRGBPalette16 currentPalette( CRGB::Black );

CRGB::Black is a constant, which, as some have pointed out is a number.

Later on in the code the author appears to write directly to currentPalette (or other similar variables) like this: currentPalette[12] = CRGB::Black;

Is currentPalette an object instance? If so then how can you access it as if it were an array?

It could be a macro in C as well. EDIT: No, it cannot. But, having looked at the rest of the code, I do believe it is indeed C++. — John Go-Soco
– John Go-Soco, Commented Sep 26, 2018 at 10:51
Are you sure CRGB::Black is actually a struct and not an enum constant? — HolyBlackCat
– HolyBlackCat, Commented Sep 26, 2018 at 10:51
@wildplasser: It is Arduino Language, which is an unspecified, undocumented (basically "whatever the Arduino IDE will accept") close relative of C++. The actual compiler is a fork of GCC, but the IDE does some preprocessing and wrapping of the code (for example generating a suitable main method). — Jörg W Mittag
– Jörg W Mittag, Commented Sep 26, 2018 at 11:04
CRGB::Black is a number, not a struct. There are many constructors for CRGBPalette16, with varying numbers of parameters. Related: FastLED reference. — molbdnilo
– molbdnilo, Commented Sep 26, 2018 at 11:05

John Go-Soco · Accepted Answer · 2018-09-26 10:49:06Z

4

Having had a look at the rest of the file, I believe you are looking at some C++ code.

CRGBPalette16 currentPalette( CRGB::Black );

This line initialises an object of type CRGBPalette16 with the enum parameter CRGB::Black.

You can see the object passed as a reference into other functions, such as here on line 72:

leds[i] = ColorFromPalette( currentPalette, colorIndex + sin8(i*16), brightness);

answered Sep 26, 2018 at 10:49

John Go-Soco

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3 Comments

Tom Auger Over a year ago

Thanks. So CRGBPalette16 is an object and we're calling its constructor here? It's weird, because you can assign directly to it like: currentPalette[12] = 0xffcc88;

John Go-Soco Over a year ago

Not weird at all because you can define an overload operator for objects. Have a look at learncpp.com/cpp-tutorial/98-overloading-the-subscript-operator

John Go-Soco Over a year ago

EDIT: Just realised my mistake there in my last comment. It should say "You can define an overload to the subscript operator for objects".

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