Copying struct with array

[David Rasmussen]

If I have this

struct S
{
int arr[5];
};

and I do this:

S s1,s2;

....

s1 = s2;

what happens?

Normally, array assignments aren't possible/allowed. If I do s1.arr =
s2.arr I get a compiler error. If I do s1 = s2 it compiles fine. And it
even seems like the array is getting copied, not just the pointer to the
start of the array, at least with g++.

Is there any difference in semantics here betweeen C and C++?

/David

[Andrey Tarasevich]

JKop wrote:

Now, take your example:

s1.ar = s2.ar;

That is equal to:

&s1.ar[0] = &s2.ar[0];

That's exactly like writing:

unsigned int k = 4;
&k = 27873;

You're not changing the value of a variable at all! You're trying to change
the address of a variable! Self-explanatory I hope!
...

This doesn't really explain much. Yes, the standard array-to-pointer
conversion is the immediate formal reason why such code won't compile,
but the _real_ question is why array assignment (and array copying)
contexts were not excluded from the list of contexts where
array-to-pointer conversion is applied. Today there is no formal reason
for it to be this way, although there probably was one a rather long
time ago.

There is no technical problems with requiring the language to perform
array assignment in

s1.ar = s2.ar;

But doing this will break the compatibility with previous version of
language specification.

Note also that one specific array-related context does actually copy arrays:

char lpsz[] = "Hello world";

--
Best regards,
Andrey Tarasevich