[Gambas-user] Memory Stream Help

[Benoît Minisini]

Le 22/11/2011 18:56, Randall Morgan a écrit :
> I do the C structures defined. But the functions return pointers to the
> structures created by Tidy. So I have to Read the data into my local copy
> using the pointer returned. Which I feel is very inefficient. I have just
> started to play around with defining offset values for each location in the
> structure returned by tidy and simply accessing tidy's structures directly.
> I feel this is more efficient that making local copies of the structures.
>
> I am new to Gambas but not programming in general. So any pointer on how
> best to work with external libraries would be helpful. Once I have a well
> defined interface to the external library I want to package it as a
> component. There other external libraries I'd like to package as components
> as well. So this is just my first attempted. I've had some minor successes
> so far. But I want to make the library wrapper as useful as possible by
> including at least a reasonable subset of Tidy's capabilities.
>
> I would love to see some Gambas 3 samples code for reading and writing
> c-structures using pointers....
>
>

Hi,

In revision #4257, I have added support for extern functions that return 
a pointer to a C structure.

So...

To send a structure pointer to an extern function, do that:

--8<-----------------------------------------------------------------
Public Struct StructTm
   tm_sec As Integer
   tm_min As Integer
   tm_hour As Integer
   tm_mday As Integer
   tm_mon As Integer
   tm_year As Integer
   tm_wday As Integer
   tm_yday As Integer
   tm_isdst As Integer
End Struct

Private Extern asctime(tm As StructTm) As String In "libc:6"
--8<-----------------------------------------------------------------

And to get a structure pointer from an extern function, do that:

--8<-----------------------------------------------------------------
Public Struct StructTm
   tm_sec As Integer
   tm_min As Integer
   tm_hour As Integer
   tm_mday As Integer
   tm_mon As Integer
   tm_year As Integer
   tm_wday As Integer
   tm_yday As Integer
   tm_isdst As Integer
End Struct

Private Extern localtime(timep As Pointer) As StructTm In "libc:6"
--8<-----------------------------------------------------------------

A temporary Gambas structure object is allocated each time the 
localtime() is called. It stores the return value, but it does not copy 
the structure data, it just points at it. So the pointed structure must 
not be freed while you are using it!

Does it fit your needs?

-- 
Benoît Minisini