passing an array as argument

[monkeys paw]

I am passing an array to a function. My first attempt was like so:

char *ary[] = {"an", "array"};
my_sort(ary);

But that doesn't work because the function my_sort cannot
determing the size of ary. So i had to do this:

nelems = sizeof(ary) / sizeof(char *);
my_sort(ary, nelems);

Why is this?

 

[Russell Hanneken]

I am passing an array to a function. My first attempt was like so:

char *ary[] = {"an", "array"};
my_sort(ary);

But that doesn't work because the function my_sort cannot
determing the size of ary. So i had to do this:

nelems = sizeof(ary) / sizeof(char *);
my_sort(ary, nelems);

Why is this?

This is addressed in the FAQ:

http://www.eskimo.com/~scs/C-faq/q6.21.html

 

[Barry Schwarz]

I am passing an array to a function. My first attempt was like so:

char *ary[] = {"an", "array"};
my_sort(ary);

But that doesn't work because the function my_sort cannot
determing the size of ary. So i had to do this:

nelems = sizeof(ary) / sizeof(char *);
my_sort(ary, nelems);

Why is this?

See the faq at http://www.eskimo.com/~scs/C-faq/top.html (section 6)
or google the archives. This gets discussed at least monthly.


<<Remove the del for email>>

 

[macluvitch]

keep in mind that the size of a pointer is 4 bytes in a 64bit system

the prototype of myµ_sort should be sth like

return type my_sort (char **ary,.......)

 

[Richard Bos]

keep in mind that the size of a pointer is 4 bytes in a 64bit system

Or better, do not; the Standard says nothing about the size of pointers,
and in fact it's quite possible for pointers to different types to be
different sizes.

the prototype of myµ_sort should be sth like

return type my_sort (char **ary,.......)

That's not a prototype, it's a return statement, and a broken one at
that.

Richard

 

[Dan Pop]

keep in mind that the size of a pointer is 4 bytes in a 64bit system

Engage your brain and explain to the rest of us how can a 4-byte pointer
cover a 64-bit address space.

It is possible to use 64-bit hardware in 32-bit mode (as older OpenVMS
versions and Windows/NT did on Alpha and older IRIX versions did on MIPS
4000 and above), but the resulting system does NOT qualify as a 64-bit
system.

For a C implementation to qualify as a 64-bit implementation, it needs
64-bit pointers and at least one standard 64-bit integer type. gcc on
64-bit Linux systems has 64-bit pointers and longs (it uses the
I32LP64 model, according to a common jargon).

Dan

 

[Ben Pfaff]

Engage your brain and explain to the rest of us how can a 4-byte pointer
cover a 64-bit address space.

With 16-bit bytes?

 

[Stephen Sprunk]

In <e78e777a530ff915bf43f18fd1e815b0@localhost.talkaboutprogramming.com>

Engage your brain and explain to the rest of us how can a 4-byte pointer
cover a 64-bit address space.

Well, CHAR_BIT could be 16

It is possible to use 64-bit hardware in 32-bit mode (as older OpenVMS
versions and Windows/NT did on Alpha and older IRIX versions did on MIPS
4000 and above), but the resulting system does NOT qualify as a 64-bit
system.

For a C implementation to qualify as a 64-bit implementation, it needs
64-bit pointers and at least one standard 64-bit integer type. gcc on
64-bit Linux systems has 64-bit pointers and longs (it uses the
I32LP64 model, according to a common jargon).

Would you consider an IP32L64 system as 64-bit? It's certainly possible to
implement a "tiny" memory model for AMD64, giving you the better memory
efficiency of 32-bit pointers while retaining access to features not
available in 32-bit mode. And even in the small and kernel code models,
function pointers need only be 32-bit anyway, with a sign extension if
converted to a void pointer.

S

 

[Martin Ambuhl]

Engage your brain and explain to the rest of us how can a 4-byte pointer
cover a 64-bit address space.

By using 16-bit bytes, obviously.

 

[Dan Pop]

With 16-bit bytes?

I was talking about *existing*, *real life*, 64-bit implementations, as I
assumed the previous poster did, rather than pipe dream ones.

Dan

 

[Dan Pop]

Would you consider an IP32L64 system as 64-bit?

To the same extent that an IP16L32 system could be considered as 32-bit.

Dan

 

[Guillaume]

Engage your brain and explain to the rest of us how can a 4-byte pointer

By using 16-bit bytes, obviously.

Clever.

 

[macluvitch]

That's not a prototype, it's a return statement, and a >broken one at
that.

yo folk what going on with you
I meant by return type the function return type


I think that pointers size in memory has sth with the current os file
system

 

[Keith Thompson]

That's not a prototype, it's a return statement, and a broken one at
that.

I think "macluvitch" meant the phrase "return type" to stand in for
the return type of the function. It would have been clearer as:

RETURN_TYPE my_sort (char **ary, .......)

(When we see the word "return" in C code or pseudo-code, we naturally
assume that it's the C keyword.)