What does a dot before the variable name in struct mean?
This is a Designated Initializer, which is syntax added for C99.Relevant excerpt:
In a structure initializer, specify the name of a field to initializewith ‘.fieldname =’ before the element value. For example, given thefollowing structure,
struct point { int x, y; }; the following initialization
struct point p = { .y = yvalue, .x = xvalue }; is equivalent to
struct point p = { xvalue, yvalue };