On Tue, 12 Jul 2011 15:59:58 +0100, Steven Schveighoffer
<[email protected]> wrote:
On Tue, 12 Jul 2011 10:50:07 -0400, Regan Heath <[email protected]>
wrote:
What if you expect the function is expecting to write to the buffer,
and the compiler just made a copy of it? Won't that be pretty
surprising?
Assuming a C function in this form:
void write_to_buffer(char *buffer, int length);
No, assuming C function in this form:
void ucase(char* str);
Essentially, a C function which takes a writable already-null-terminated
string, and writes to it.
Ok, that's an even better example for my case.
It would be used/called like...
char[] foo;
.. code which populates foo with something ..
ucase(foo);
and in D today this would corrupt memory. Unless the programmer
remembered to write:
ucase(toStringz(foo));
So, +1 for compiler called toStringz.
I am assuming also that if this idea were implemented it would handle
things intelligently, like for example if when toStringz is called the
underlying array is out of room and needs to be reallocated, the compiler
would update the slice/reference 'foo' in the same way as it already does
for an append which triggers a reallocation.
You might initially extern it as:
extern "C" void write_to_buffer(char *buffer, int length);
And, you could call it one of 2 ways (legitimately):
char[] foo = new char[100];
write_to_buffer(foo, foo.length);
or:
char[100] foo;
write_to_buffer(foo, foo.length);
and in both cases, toStringz would do nothing as foo is zero terminated
already (in both cases), or am I wrong about that?
In neither case are they required to be null terminated.
True, but I was outlining the worst case scenario for my suggestion, not
describing the real C function requirements.
In this particular case the extern "C" declaration (IMO) for this style of
function should be one of:
extern "C" void write_to_buffer(ubyte *buffer, int length);
extern "C" void write_to_buffer(byte *buffer, int length);
extern "C" void write_to_buffer(void *buffer, int length);
which would all be ignored by my suggestion.
The only thing that guarantees null termination is a string literal.
string literals /and/ calling toStringz.
Even "abc".dup is not going to be guaranteed to be null terminated. For
an actual example, try "012345678901234".dup. This should have a 0x0f
right after the last character.
Why 0x0f? Does the allocator initialise array memory to it's offset from
the start of the block or something?
I have just realised that char is initialised to 0xFF. That is a problem
as my two examples above would be arrays full of 0xFF, not \0.. meaning
toStringz would have to reallocate to append \0 to them, drat. That is
yet another reason to use ubyte or byte when interfacing with C.
Ok, how about going the other way. Can we have something to decorate
extern "C" function parameters to trigger an implicit call of toStringz on
them?
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