[Gambas-user] [Fwd: Gambas3 Pointers example] signal #6

[Demosthenes Koptsis]

Here is a last case about pointers i found.

CASE 1
-------
When a C++ function does not malloc any memory it may return a pointer.
In this case we can do

DIM pPointer as Pointer
pPointer = Alloc(4096)' alloc 4096 bytes

pPointer = getwd(pBuf)

'use pPointer with Str@() or other xxx@()

Free(pPointer)
pPointer=0

OK!

CASE 2
-------
When a c++ function itself allocate memory with malloc() what can we do?

Example.
--------
' Gambas module file
'char *get_current_dir_name(void);
Extern get_current_dir_name() As Pointer In "libc:6"

Public Sub Main()

  Dim pFunc As Pointer
  Dim sWorkingDirectory As String

'get_current_dir_name
  pFunc = Alloc(4096)
  Print pFunc '0xc12938
  
  pFunc = get_current_dir_name()
  Print pFunc '0xc147a0
  
  'now we cannot Free(pFunc) it is not 0xc12938 anymore
  'get_current_dir_name() malloc itself memory and return a new pointer
   
  sWorkingDirectory = Str@(pFunc)
  Print sWorkingDirectory

' Free(pFunc)
'if i unrem Free i get a crash, because i try to free the 0xc147a0
  pFunc = 0

End

What can we do in such cases when a function itself allocates memory?
Should we free it? Can we?

May be we can use pointers without Alloc()?

Example, no Alloc(), no Free, just DIM pPointer
---------
' Gambas module file
'char *get_current_dir_name(void);
Extern get_current_dir_name() As Pointer In "libc:6"

Public Sub Main()

  Dim pFunc As Pointer
  Dim sWorkingDirectory As String

'get_current_dir_name
  
  pFunc = get_current_dir_name()
  Print pFunc '0xc147a0
  
  sWorkingDirectory = Str@(pFunc)
  Print sWorkingDirectory

  pFunc = 0

End