p[assing by reference

[realgeek]

I am novice to C; or rather I have forgoteen C long ago cause I'm a
young programmer and i didn't do much of it.
I have int *a; int l;
I have some logic that creates an array of arbitrary length in a
function and I want it to stick it into a and its length into l.

I have the following function now:
int* ReadArray(int &l)
{
//do stuff
}

int *a;
int l;
a = ReadArray(l);

GCC 3.2 tells me I have "parse error before '&' token" on the line
where the function is declared.
I don't understand, my memory and examples on the internet tell me in
unison that it's the way to pass stuff by reference. Or at least to
declare it. What's wrong with it/how do I do it right?

[Lew Pitcher]

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re******@gmail.com wrote:

I am novice to C; or rather I have forgoteen C long ago cause I'm a
young programmer and i didn't do much of it.
I have int *a; int l;
I have some logic that creates an array of arbitrary length in a
function and I want it to stick it into a and its length into l.

I have the following function now:
int* ReadArray(int &l)
{
//do stuff
}

int *a;
int l;
a = ReadArray(l);

GCC 3.2 tells me I have "parse error before '&' token" on the line
where the function is declared.
Yup. You do.
I don't understand, my memory and examples on the internet tell me in
unison that it's the way to pass stuff by reference.
C doesn't support passing data "by reference". The best you can get from
C is pass "by value".
Or at least to
declare it. What's wrong with it/how do I do it right?

You are writing C++ code, and trying to compile it as C code.

- --

Lew Pitcher, IT Specialist, Corporate Technology Solutions,
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
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[realgeek]

Umm... how do I achieve that kind of thing then? I am also intending to
use function to read x-y sized matrix from a file, where x and y are in
that same file, I have to return its dimensions with it; I oculd stick
them intto int*, but is there a better way?

[Vladimir S. Oka]

On Thursday 09 March 2006 20:27, re******@gmail.com opined (in
<11**********************@j33g2000cwa.googlegroups .com>):

I am novice to C; or rather I have forgoteen C long ago cause I'm a
young programmer and i didn't do much of it.
I have int *a; int l;
I have some logic that creates an array of arbitrary length in a
function and I want it to stick it into a and its length into l.

I have the following function now:
int* ReadArray(int &l)
{
//do stuff
}

int *a;
int l;
a = ReadArray(l);

GCC 3.2 tells me I have "parse error before '&' token" on the line
where the function is declared.
I don't understand, my memory and examples on the internet tell me in
unison that it's the way to pass stuff by reference. Or at least to
declare it. What's wrong with it/how do I do it right?

If you want to get answers in c.l.c, you should follow some simple
guidelines for posting and topicality. For the posting, read:
<http://cfaj.freeshell.org/google/>. For the topicality and etiquete
read: <http://clc-wiki.net/wiki/Introduction_to_comp.lang.c>.

One reason for me telling you this is that in your reply to Lew, you did
not quote what and who you were replying to. That is a Very Bad Thing.

Back to your problem...

Apart from what you were already told, you may achieve what you want by
re-phrasing your code like this:

int* ReadArray(int &l)
{
/* do stuff, but using *l instead of l */
}

int *a;
int l;
a = ReadArray(&l);

This simulates "pass by reference" at the cost of typing '*l' where
you'd want just 'l'. C always passes "by value", but you can pass a
pointer and change the original through it.

--
BR, Vladimir

H. L. Mencken suffers from the hallucination that he is H. L.
Mencken -- there is no cure for a disease of that magnitude.
-- Maxwell Bodenheim

[c.anoop]

int * ReadArray(int *l)
{
// do stuff
}
main()
{
int *a;
int l;
a = ReadArray(&l);
}
this is the normal way in c.
But if u want to return the dimentions along with array use a struct
defined as
struct a {
int row;
int column;
int *array;
};
create the array and struct dynamically using malloc
or calloc and return the address of the struct.

[Keith Thompson]

re******@gmail.com writes:

Umm... how do I achieve that kind of thing then? I am also intending to
use function to read x-y sized matrix from a file, where x and y are in
that same file, I have to return its dimensions with it; I oculd stick
them intto int*, but is there a better way?

Achieve what kind of thing?

Please read <http://cfaj.freeshell.org/google/> if you want anyone to
know what you're talking about.

C doesn't directly support pass-by-reference, only pass-by-value. You
can achieve the effect of pass-by-reference by passing a pointer (the
pointer is passed by value).

The unary "&" operator yields the address of its operand (i.e., a
pointer to it). The unary "*" operator dereferences a pointer (i.e.,
it yields the value of the object it points to).

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Keith Thompson]

"Vladimir S. Oka" <no****@btopenworld.com> writes:
[...]

Apart from what you were already told, you may achieve what you want by
re-phrasing your code like this:

int* ReadArray(int &l)
This should be "int *l", not "int &l".
{
/* do stuff, but using *l instead of l */
}

--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Vladimir S. Oka]

On Thursday 09 March 2006 23:05, Keith Thompson opined (in
<ln************@nuthaus.mib.org>):

"Vladimir S. Oka" <no****@btopenworld.com> writes:
[...]

Apart from what you were already told, you may achieve what you want
by re-phrasing your code like this:

int* ReadArray(int &l)

This should be "int *l", not "int &l".

{
/* do stuff, but using *l instead of l */
}

D'oh! (fx: slams head on desk) Careless copy'n'paste job.

--
BR, Vladimir

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