CODEWITHSUNDEEP
c++syntax
user1534664
user1534664

Reputation: 3418

C++ object initialisation using braces (syntax)

I just came across this line of code:

SDL_Color textColor = { 255, 0, 255 };

It made me wonder why it can be declared like an array. I thought it might've just ment the same as textColor(255,0,255); but it didnt work like that when I tried making my own class. Can anyone explain when this type of syntax is used? Where are the parameters going..?

Upvotes: 3

Views: 406

Answers (3)

juanchopanza
juanchopanza

Reputation: 227370

It is aggregate initialization of a type, most likely a simple struct or class. For example,

struct Foo 
{
  int i,j;
  double x,y;
};

int main()
{
  Foo f = {1,2, 3.,4.};
}

Note since there is some confusion regarding structs, the above example would also work with a class, which in this case is identical to the struct:

class Foo 
{
 public:
  int i,j;
  double x,y;
};

In C++11 this type of initialization is extended to non-aggregate types under certain conditions.

for example

std::vector<int> v = {1,2,3,4,5};

Upvotes: 10

Andriy
Andriy

Reputation: 8594

SDL_Color is an aggregate (a struct with 4 members, in this case).

You can initialize an aggregate (not just an array) using an initializer list.

SDL_Color textColor = { 255, 0, 255 };

is the same as

SDL_Color textColor;
textColor.r = 255;
textColor.g = 0;
textColor.b = 255;
textColor.unused = 0;

Upvotes: 1

Kerrek SB
Kerrek SB

Reputation: 476930

All aggregates can be brace-initialized, which initializes each aggregate member with the matching item. If the list contains fewer items than there are aggregate members, the remaining elements are initialized as though from an empty brace list.

Upvotes: 3

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