Initialization
A declaraton of an object may provides its initial value through the process known as initialization.
For each declarator, the initializer, if not omitted, may be one of the following:
| expression | (1) | ||||||||
{ initializer-list }
|
(2) | ||||||||
Where initializer-list is a non-empty comma-separated list of initializers (with an optional trailing comma), where each initializer has one of three possible forms:
| expression | (1) | ||||||||
{ initializer-list }
|
(2) | ||||||||
designator-list = initializer
|
(3) | ||||||||
Where designator-list is a list of either array designators of the form [ constant-expression ] or struct/union member designators of the form . identifier; see
array initialization and struct initialization
Contents |
Explanation
The initializer specifies the initial value stored in an object.
If an initializer is provided, see
- scalar initialization for the initialization of scalar types
- array initialization for the initialization of array types
- struct initialization for the initialization of struct and union types.
If an initializer is not provided,
- objects with automatic storage duration are initialized to indeterminate values (which may be trap representations)
- objects with static and thread-local storage duration are initialized as follows
- pointers are initialized to null pointer values of their types
- objects of integral types are initialized to unsigned zero
- objects of real types are initialized to positive zero
- members of arrays, structs, and unions are initialized as described above, recursively, and all padding bits are initialized to zero
Notes
When initializing an object of static or thread-local storage duration, every expression in the initializer must be a constant expression or string literal.
Initializers cannot be used in declarations of objects of incomplete type, VLAs, and block-scope objects with linkage.
The initial values of function parameters are established as if by assignment from the arguments of a function call, rather than by initialization.
Example
{{example
| code=
int a[2]; // initializes a to {0, 0} int main(void) {
// initializes n to 1 int n = 1;
// initializes int x[3] to 1,2,3
// initializes int* p to &x[0]
int x[] = { 1, 3, 5 }, *p = x;
// initialize w (an array of two structs) to
// { {{1,0,0}, 0}, {{2,0,0}, 0} }
struct {int a[3], b;} w[] = {[0].a = {1}, [1].a[0] = 2};
} }}
See also
| C++ documentation for initialization
|
