CODEWITHSUNDEEP
cmemory-managementstructdynamic-memory-allocationcalloc
platinoob_
platinoob_

Reputation: 161

Allocate a structure by calloc(): To which value the members are initialized?

For example I have a struct

struct s{
    char c;
    int x;
};

And I use calloc() to allocate memory.

s *sp = (s*) calloc(1, sizeof(s));

Now, what will be the values of sp->c and sp->x?

Upvotes: 0

Views: 2305

Answers (1)

RobertS supports Monica Cellio
RobertS supports Monica Cellio

Reputation: 15062

"What will be the values of sp->c and sp->x?"

Since calloc() sets all bits of the allocated memory to 0, c and x will have the value of 0 if the 0 value representation of int and char is of all bits to 0 (which is common).

Note that in the case of pointers, the pointer might not be standard-compliant NULL pointer when just setting all bits to 0 as the C standard does not require the representation of NULL pointers to be all-zero-bits.

Side notes:

1.

struct s{
    char c;
    int x;
};

s *sp = (s*) calloc(1, sizeof(s));

can´t work as s isn´t a typedefd type; it is a structure tag. Therefore, You need to precede s by the struct keyword:

struct s *sp = (struct s*) calloc(1, sizeof(struct s));

2.

You do not need to cast the returned pointer from calloc() and other memory management functions and rather avoid it since it can add clutter to your code. -> Do I cast the result of malloc

So, just do:

struct s *sp = calloc(1, sizeof(struct s));

Upvotes: 2

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