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From: bart <bc@freeuk.com>
Newsgroups: comp.lang.c
Subject: =?UTF-8?Q?Re=3A_technology_discussion_=E2=86=92_does_the_world_need?=
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Date: Wed, 10 Jul 2024 13:51:02 +0100
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On 10/07/2024 00:35, Ben Bacarisse wrote:
> bart <bc@freeuk.com> writes:
> 
>> On 09/07/2024 18:22, Ben Bacarisse wrote:
>>> bart <bc@freeuk.com> writes:
>>>
>>>> On 09/07/2024 16:58, Ben Bacarisse wrote:
>>>>> bart <bc@freeuk.com> writes:
>>>>>
>>>>>> Arrays are passed by reference:
>>>>>>
>>>>>>      void F(int a[20]) {}
>>>>>>
>>>>>>      int main(void) {
>>>>>>        int x[20];
>>>>>>        F(x);
>>>>>>      }
>>>>> This is the sort of thing that bad tutors say to students so that they
>>>>> never learn C properly.  All parameter passing in C is by value.  All of
>>>>> it.  You just have to know (a) what the syntax means and (b) what values
>>>>> get passed.
>>>>
>>>> The end result is that a parameter declared with value-array syntax is
>>>> passed using a reference rather than by value.
>>>>
>>>> And it does so because the language says, not because the ABI requires
>>>> it. A 2-byte array is also passed by reference.
>>> An address value is passed by value.  C has only one parameter passing
>>> mechanism.  You can spin it as much as you like, but C's parameter
>>> passing is simple to understand, provided learner tune out voices like
>>> yours.
>>
>> Little about C's type system is simple.
> 
> Parameter passing is relatively simple though since there is only one
> mechanism -- pass by value.

Except when it comes to arrays. Obviously arrays aren't passed by value, 
but that's because of X and Y.

What would be genuinely simple is:

    void F(T x) {}
    void G(T* y) {}

where an object of type T is always passed by value, and that of type T* 
always passes a pointer to the value. Here, T represents exactly the 
same type as when it used outside a parameter list:

    T a;
    T* p;

but only in the context of C is it necessary to mention that, since it 
C, that may not be the case.

(The mechanisms of the underlying ABI do not affect this; they just make 
implementation harder.)

>> You're doing your students a
>> disservice if you try and hide all the quirks.
> 
> If.  Always with the if.  There are lots of things I don't do that would
> be doing my students a disservice were I to do them.  Beautiful spin!


Have a look at forums like the Reddit one on C programming, to see the 
kinds of things that people learning C get confused about. Lots of them 
are to do with the funny quirks of C, and a big proportion are due to 
how arrays and pointers are so intertwined in that language.

Well, C can't be fixed. But what would you do: explain the flaws in the 
language, the discontinuities, or brush them under the carpet?

Or maybe explain the quirks, but pretend they are by design?

What I find especially wonderful is that every time you see a pointer 
type like T*, C gives you an extra array dimension on top, whether or 
not T actually points to the first element of an array.

So you never know whether T* is intended to represent a 0- or 
1-dimensioned object, or a 1- or 2-dimensioned one.

And what I find frustrating is that people learning C get the idea that 
all this quirkiness goes hand-in-hand with lower-level programming.