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digitalmars.D.learn - how to pass a ubyte[] to c interface?

reply "zhmt" <zhmtzhmt qq.com> writes:
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?
Mar 12 2015
next sibling parent "zhmt" <zhmtzhmt qq.com> writes:
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");
	}
Mar 12 2015
prev sibling next sibling parent reply Rikki Cattermole <alphaglosined gmail.com> writes:
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*) {
	// ...
}
Mar 12 2015
parent reply "zhmt" <zhmtzhmt qq.com> writes:
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.
Mar 12 2015
parent Rikki Cattermole <alphaglosined gmail.com> writes:
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.
Mar 12 2015
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
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
Mar 12 2015
parent "zhmt" <zhmtzhmt qq.com> writes:
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.
Mar 13 2015