Re: Promoting unsigned long int to long int

On Jun 30, 11:13 pm, Keith Thompson <ks...@xxxxxxx> wrote:

size_t can represent the size in bytes of any object (since it's the
type of the result of the sizeof operator and of the argument to
malloc(). It can therefore represent the size in elements of any
array object, making it suitable for array indices.

The third is a bit more iffy; it depends on what you're counting.

But there are no such guarantees for unsigned long. Consider a
hypothetical system where unsigned long is 32 bits and size_t is 64
bits. You might have objects whose size cannnot be represented as an
unsigned long value.

The question is, why would you want to use unsigned long rather than
size_t?

Suppose I have a structure:

struct mesh
{
unsigned long nvert; /* number of vertices */
unsigned long ntri; /* number of triangles */
vector *vert; /* pointer to array of vertices */
triangle *tri; /* pointer to array of triangles */
};

Now, according to what you are saying nvert and ntri should have data
type size_t instead. In my program its possible for nvert and ntri to
be in millions. I have been adviced that size_t in many cases causes
loss of data, hence I'm skecptical about its use. Also, I would want
to keep things consistent.
.