C struct automatic initialization values, array initializations

Question

If I were to have two structs

typedef struct {
  int number_of_lines;
  char lines[MAX_CHAPTER_LINES][MAX_STR_SIZE + 1];
} Chapter;

typedef struct {
  char name         


        

Answer 1

It depends. Unless initialized explicitly,

• If the variable has static (or thread) storage duration, the members will be initialized to 0 or equivalent.

• In case it has automatic storage duration, the contents will be left indeterminate (yes, "indeterminate" is more appropriate than "garbage").

Quoting C11, chapter §6.7.9/p10

If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. If an object that has static or thread storage duration is not initialized explicitly, then:

— if it has pointer type, it is initialized to a null pointer;

— if it has arithmetic type, it is initialized to (positive or unsigned) zero;

— if it is an aggregate, every member is initialized (recursively) according to these rules, and any padding is initialized to zero bits;

— if it is a union, the first named member is initialized (recursively) according to these rules, and any padding is initialized to zero bits;