Free memory from a string used in a structure?

[Mistrel]

How does this work? I know some people here have solved this in the past but the method eludes me.

Code: Select all

Structure That
  Fred.s
EndStructure

Repeat
  *This.That=AllocateMemory(SizeOf(That))
  *This\Fred="Hello, Fred!"
  *This\Fred=#NULL$
  FreeMemory(*This)
ForEver

[Demivec]

Here's freak's solution:

Code: Select all

Procedure FreePBString(*Address)
  Protected string.String  ; the String Structure contains one String element, which is initialized to 0 on procedure start
  PokeL(@string, *Address) ; poke our strings address into the structure
EndProcedure               ; when returning, PB's string free routine for the local structure will actually free the passed string.

and here's how you would use it in your sample code:

Code: Select all

Structure That
  Fred.s
EndStructure

Repeat
  *This.That=AllocateMemory(SizeOf(That))
  *This\Fred="Hello, Fred!"
  FreePBString(@*This\Fred)
  FreeMemory(*This)
ForEver

A search on freeing strings would have brought up several threads.

@Edit: added a missing "*" to the code sample. Thanks flaith and Mistrel.

[srod]

Yes I use this little routine all the time - very useful!

[Mistrel]

Thank you. This is exactly what I was looking for.

[flaith]

FreePBString(@This\Fred)

Maybe it should be

Code: Select all

FreePBString(*@This\Fred)

[Mistrel]

FreePBString(@This\Fred)

Maybe it should be

Code: Select all

FreePBString(*@This\Fred)

Maybe it should be

Code: Select all

FreePBString(@*This\Fred)

[flaith]

rigth sorry

[Mahan]

A newbie PB question:

This only applies when allocating and managing structure-memory manually, right?

If I use structures with Strings in normal Lists (where the memory allocation is managed by PB), PB will surely handle the releasing of the internal strings when i do DeleteElement, correct?

[freak]

If I use structures with Strings in normal Lists (where the memory allocation is managed by PB), PB will surely handle the releasing of the internal strings when i do DeleteElement, correct?

exactly.

[mariosk8s]

Cool trick, but should that be PokeI or are strings addresses 32 bit on 64 platforms?

[Fred]

You should use ClearStructure() instead of this trick which is not granted to work with future releases. Or better if you are in PB 5.30+: uses AllocateStructure()/FreeStructure() combo.

[mariosk8s]

But i don't want to free the structure, just the string in it.

[Fred]

ClearStructure() doesn't work for you ?

[mariosk8s]

Yeah, it does, but now

Code: Select all

Structure foo
  int.i
  string.s
endstructure

becomes

Code: Select all

Structure foo
  int.i
  string.String
endstructure

And *foo\string becomes *foo\string\s.

It maskes it a bit clunky.

But then on the other hand

Code: Select all

FreePBString(@*foo\string)
PokeI(*foo+OffsetOf(foo\string), 0)

is pretty nasty, too.