[OCLUG-devel] sizeof () works differently on char's, int's, etc.

[Tim Thelin]

James Colannino wrote:

> Hey everyone.  I used the following to test how the sizeof() function 
> measures arrays of various variable types:
>
> #include <stdio.h>
>
> char  line[10];
> int   integer[10];
> float floaty[10];
>
> int main()
>
> {
>     printf ("\nCharacter: %d\n", sizeof(line));
>     printf ("Integer: %d\n", sizeof(integer));
>     printf ("Floating: %d\n\n", sizeof(floaty));
>
>     return 0;
> }
>
> My output came out as the following:
>
> Character: 10
> Integer: 40
> Floating: 40
>
> So my question is this: why does the sizeof() function work with 
> character arrays but not with numerical ones?  Is the sizeof() 
> function only intended to be used for characters and not for numbers?  
> This has me very confused.
>
> James

James,

sizeof gives back the number of bytes of storage a particular entity 
uses, not the number of elements in that entity.
So a typical use would be determining the size of a struct in bytes.  
Along those lines, your results make sense, as your 10 ints would 
consume 40 bytes of storage.

A way to get what you want, the number of elements of an array, could be 
something more like:
#define GetNumberOfElements( array )      ( sizeof( array ) / sizeof( 
array[0] ) )
That essentially gets the total bytes the array takes up, and divides it 
by the size in bytes of a single element.  The resuilt is the number of 
elements.

Thanks,
Tim Thelin