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In Cocoa programming, a designated initializer is the method through which all of the instance's initial parameters can be set. A designated initializer is typically executed implicitly when not called explicitly. In C programming, designated initializers refer to a certain way of struct/union/array initialization, which allows the programmer to to initialize an element by using its name or index.

In Cocoa programming, a designated initializer is a method that accepts all of the instance's initial parameters and initializes the instance. This method is typically something other than - (id)init, and is usually documented as the designated initializer in the header file. A designated initializer is typically executed implicitly when not called explicitly. As an example, the designated initializer of UIViewController is - (id)initWithNibName:bundle:.

In C programming, designated initializers refer to a certain way of struct/union/array initialization, which allows the programmer to to initialize an element by using its name or index. This feature was introduced with the C99 standard.

Designated initializers have two forms (ISO 9899:2011 6.7.9):

If a designator has the form
[ constant-expression ]
then the current object (defined below) shall have array type and the expression shall be an integer constant expression. If the array is of unknown size, any nonnegative value is valid.
If a designator has the form
.identifier
then the current object (defined below) shall have structure or union type and the identifier shall be the name of a member of that type.

Example of designated initializer usage (9899:2011 6.7.9/35):

struct { int a[3], b; } w[] =
       { [0].a = {1}, [1].a[0] = 2 };

In the example, both the above mentioned forms of designated initializers are combined.