Structure Initializers: Are Undefined Members Zero'd?

[Michael B Allen]

Are undefined structure members in initializers set to 0?

Consider the following code:

typedef struct fns {
int (*fn1)(int n);
int (*fn2)(int n);
int (*fn3)(int n);
int (*fn4)(int n);
int (*fn5)(int n);
} fns;
static int
my_fn1(int n)
{
....
}
static int
my_fn3(int n)
{
....
}
const fns my_fns = {
my_fn1,
NULL,
my_fn3
};

Are my_fns.fn4 and my_fns.fn5 guaranteed to be NULL here?

Mike

 

[markpapadakis]

Are undefined structure members in initializers set to 0?

Consider the following code:

typedef struct fns {
int (*fn1)(int n);
int (*fn2)(int n);
int (*fn3)(int n);
int (*fn4)(int n);
int (*fn5)(int n);
} fns;
static int
my_fn1(int n)
{
...
}
static int
my_fn3(int n)
{
...
}
const fns my_fns = {
my_fn1,
NULL,
my_fn3
};

Are my_fns.fn4 and my_fns.fn5 guaranteed to be NULL here?

Mike

According to:
http://c-faq.com/decl/initval.html
"When an automatic array or structure has a partial initializer, the
remainder is initialized to 0, just as for statics"

 

[Kevin D. Quitt]

Uninitialized and static, yes. Automatic and partially initialized, yes.

According to:
http://c-faq.com/decl/initval.html
"When an automatic array or structure has a partial initializer, the
remainder is initialized to 0, just as for statics"

More importantly, they're initialized *as if* the programmer had entered a zero constant -
so yes, pointers thus initialized are guaranteed to be NULL.