sizeof -- C Keyword

Return size of a data element

sizeof is a  C operator that returns a constant  int that gives the size of
any  given data  element.  The  element examined  can be  a data  object, a
portion of a  data object, or a type cast.   sizeof returns the size of the
element in chars; for example

    long foo;
    sizeof foo;

returns four, because a long is as long as four chars.

sizeof can also tell you the  size of an array.  This is especially helpful
for  use  with  external arrays,  whose  size  can  be  set when  they  are
initialized.  For example:

char *arrayname[] = {
    "COHERENT",
    "COHware volume I",
    "COHERENT Device Driver Kit",
        "GNU C/C++"
};

main()
{
    printf("\"arrayname\" has %d entries\n",
        sizeof(arrayname)/sizeof char*);
}

sizeof  is especially  useful in  malloc() routines, and  when you  need to
specify byte  counts to  I/O routines.   Using it to  set the size  of data
types instead of using  a predetermined value will increase the portability
of your code.

See Also

C keywords,
data types,
operators
ANSI Standard, §6.3.3.4

© 2012 by Stephen A. Ness