offsetof

offsetof (type,member)

Return member offset

This macro with functional form returns the offset value in bytes of member member in the data structure or union type type.

The value returned is an unsigned integral value of type size_t with the number of bytes between the specified member and the beginning of its structure.

Parameters

type: A type in which member is a valid member designator.

type shall be a structure or union type.

type shall be a POD class (including unions).

type shall be a standard-layout class (including unions).
member: A member of type.

Return value

A value of type size_t with the offset value of member in type.

Example

/* offsetof example */
#include <stdio.h> /* printf */
#include <stddef.h> /* offsetof */
struct foo {
 char a;
 char b[10];
 char c;
};
int main ()
{
 printf ("offsetof(struct foo,a) is %d\n",(int)offsetof(struct foo,a));
 printf ("offsetof(struct foo,b) is %d\n",(int)offsetof(struct foo,b));
 printf ("offsetof(struct foo,c) is %d\n",(int)offsetof(struct foo,c));
 
 return 0;
}

Output:

offsetof(struct foo,a) is 0
offsetof(struct foo,b) is 1
offsetof(struct foo,c) is 11

Exceptions

No-throw guarantee: this macro never throws exceptions: noexcept(offsetof(type,member)) is always true.

macros

types

offsetof

Parameters

Return value

Example

Exceptions