ubyte[] arr ;

I pass the arr.ptr to c program, it fails silently.

Is there any way to cast a ubyte[] to a clang pointer?

I have some source code of vibe.d, it does this in the same way, and it works .

void read(ubyte[] dst)
	{
		checkConnected(false);
		acquireReader();
		scope(exit) releaseReader();
		while (dst.length > 0) {
			checkConnected(false);
			logTrace("evbuffer_read %d bytes (fd %d)", dst.length, m_ctx.socketfd);
			auto nbytes = bufferevent_read(m_ctx.event, dst.ptr, dst.length);
			logTrace(" .. got %d bytes", nbytes);
			dst = dst[nbytes .. $];

			if( dst.length == 0 ) break;

			checkConnected(false);
			m_ctx.core.yieldForEvent();
		}
		logTrace("read data");
	}

On 13/03/2015 7:35 p.m., zhmt wrote:
> ubyte[] arr ;
>
> I pass the arr.ptr to c program, it fails silently.
>
> Is there any way to cast a ubyte[] to a clang pointer?

Theoretically this should work.

D:

void func(ubyte[] value) {
	func(value.length, value.ptr);
}

extern(C) void func(size_t length, ubyte*);

C:
void func(size_t length, ubyte*) {
	// ...
}

On Friday, 13 March 2015 at 06:39:31 UTC, Rikki Cattermole wrote:
> On 13/03/2015 7:35 p.m., zhmt wrote:
>> ubyte[] arr ;
>>
>> I pass the arr.ptr to c program, it fails silently.
>>
>> Is there any way to cast a ubyte[] to a clang pointer?
>
> Theoretically this should work.
>
> D:
>
> void func(ubyte[] value) {
> 	func(value.length, value.ptr);
> }
>
> extern(C) void func(size_t length, ubyte*);
>
> C:
> void func(size_t length, ubyte*) {
> 	// ...
> }

Thank you for your confirm,I will try again.

On 13/03/2015 7:47 p.m., zhmt wrote:
> On Friday, 13 March 2015 at 06:39:31 UTC, Rikki Cattermole wrote:
>> On 13/03/2015 7:35 p.m., zhmt wrote:
>>> ubyte[] arr ;
>>>
>>> I pass the arr.ptr to c program, it fails silently.
>>>
>>> Is there any way to cast a ubyte[] to a clang pointer?
>>
>> Theoretically this should work.
>>
>> D:
>>
>> void func(ubyte[] value) {
>>     func(value.length, value.ptr);
>> }
>>
>> extern(C) void func(size_t length, ubyte*);
>>
>> C:
>> void func(size_t length, ubyte*) {
>>     // ...
>> }
>
> Thank you for your confirm,I will try again.

Just be careful about GC pointers. They could be free'd and the c library thinks it is still live.
Either keep a copy of the pointer alive on the heap somewhere or tell the GC to ignore it.

On 03/12/2015 11:35 PM, zhmt wrote:

> ubyte[] arr ;
>
> I pass the arr.ptr to c program

Unless there is sentinel value at the end of the array, you must also pass the number of elements (as Rikki Cattermole has shown).

However, if the C function holds on to that pointer for later use, you must also keep the array alive. You can ensure that by two general ways:

a) The D-side slice must not be a local slice. For example, it can be a member of a long-living object or it is a module-scope variable.

b) Tell the garbage collector that there is indeed a reference to that memory block somewhere else (even though there is no D-side reference to it). You can do this with GC.addRoot. (The opposite function is GC.removeRoot.)

>, it fails silently.

That's not good.

> Is there any way to cast a ubyte[] to a clang pointer?

Going off-topic, I think you mean the C language when you say "clang", which may be confusing because there is also the compiler called clang. :)

Ali

On Friday, 13 March 2015 at 06:56:33 UTC, Ali Çehreli wrote:
> On 03/12/2015 11:35 PM, zhmt wrote:
>
> > ubyte[] arr ;
> >
> > I pass the arr.ptr to c program
>
> Unless there is sentinel value at the end of the array, you must also pass the number of elements (as Rikki Cattermole has shown).
>
> However, if the C function holds on to that pointer for later use, you must also keep the array alive. You can ensure that by two general ways:
>
> a) The D-side slice must not be a local slice. For example, it can be a member of a long-living object or it is a module-scope variable.
>
> b) Tell the garbage collector that there is indeed a reference to that memory block somewhere else (even though there is no D-side reference to it). You can do this with GC.addRoot. (The opposite function is GC.removeRoot.)
>
> >, it fails silently.
>
> That's not good.
>
> > Is there any way to cast a ubyte[] to a clang pointer?
>
> Going off-topic, I think you mean the C language when you say "clang", which may be confusing because there is also the compiler called clang. :)
>
> Ali


sorry for "clang", I mean c , not clang of mac.

Thanks for you advice, I use coroutine, so the array will hold in stack, will not be gc before return.

And I successfully passed the arr.ptr to c program. I found the root of problem:
The order of method declaration in c++ class and d interface must be exactly the same:

this is d code:

        interface CConn
	 {
		void free();
		int connect(ubyte* ip,int port,CFiberCtx fiberctx);
		int read(ubyte* buf,int offset, int len,CFiberCtx fiberctx);
		int readSome(ubyte* buf,int offset, int len,CFiberCtx fiberctx);
		int write(ubyte* buf,int offset, int len,CFiberCtx fiberctx);
	}

this is c++ class:

class CConn
{
public:
  //==== dlang interfaces;
  virtual void free();
  virtual int connect(char* ip,int port,CFiberCtx *fiberctx);
  virtual int read(char* buf,int offset, int len,CFiberCtx *fiberctx);
  virtual int write(char* buf,int offset, int len,CFiberCtx *fiberctx); //ERROR : swap this line with below, everything will be ok
  virtual int readSome(char* buf,int offset, int len,CFiberCtx *fiberctx);
}

After swapping the last two lines, everything goes well.

The tutorial of d dont mention this.

Thanks for all replies.