Question

While reading a code I came across, the following definition and initialization of a struct:

// header file
struct foo{
char* name;
int value;
};

//Implementation file
struct foo fooElmnt __foo;
// some code using fooElmnt
struct foo fooElmnt __foo = {
    .name = "NAME";
    .value = some_value;
}

What does this mean in C and how is it different from usual declarations?

Answer 1

It’s called designated initialization,

In a structure initializer, specify
the name of a field to initialize with
.fieldname = before the element
value. For example, given the
following structure,

 struct point { int x, y; };

the following initialization

 struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

 struct point p = { xvalue, yvalue };

If you read on, it explains that .fieldname is called a designator.

UPDATE: I’m no C99 expert, but I couldn’t compile the code. Here’s the changes I had to make:

// header file
struct foo{
char* name;
int value;
};

//Implementation file
//struct foo fooElmnt __foo;
// some code using fooElmnt
struct foo fooElmnt  = {
    .name = "NAME",
    .value = 123
};

Were you able to compile it? I used TCC.