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In C99 (and not in C++), it's possible to initialize structs using this syntax:
struct info
{
char name[8+1];
int sz;
int typ;
};
struct info arr[] =
{
[0] = { .sz = 20, .name = "abc" },
[9] = { .sz = -1, .name = "" }
};
What happens to the unspecified fields?
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A designated initializer, or designator, points out a particular element to be initialized. A designator list is a comma-separated list of one or more designators. A designator list followed by an equal sign constitutes a designation.
Designated initialization is an extension of aggregate initialization and empowers you to directly initialize the members of a class type using their names. Designated initialization is a special case of aggregate initialization.
Designated initializers are the primary initializers for a class. A designated initializer fully initializes all properties introduced by that class and calls an appropriate superclass initializer to continue the initialization process up the superclass chain.
Initializer. In C/C99/C++, an initializer is an optional part of a declarator. It consists of the '=' character followed by an expression or a comma-separated list of expressions placed in curly brackets (braces).
They are zeroed. From the C99 standard §6.7.8 (Initialization)/21,
If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.
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