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Active Forums => Programs => Topic started by: bplus on September 06, 2019, 05:26:39 pm

Title: My First Attempt with MEM
Post by: bplus on September 06, 2019, 05:26:39 pm
I see a future need to copy a SINGLE array to another, so I tried Steve's lesson on MEM, it worked!

I tried to extend it to strings?, nope, fixed strings? nope, unless I am doing something wrong?

Code: QB64: [Select]
  1. _TITLE "Mem test for array copy" 'B+ 2019-09-06
  2. DIM a(1 TO 20), a1(1 TO 20) AS STRING * 100 'cant do variable length strings , apparently not fixed strings either
  3. REDIM bCopy(0), b1Copy(0) AS STRING * 100
  4.  
  5. FOR i = 1 TO 20
  6.     a(i) = INT(10000 * RND) / 100
  7.     a1(i) = STR$(a(i))
  9.  
  10. sngArrCopy a(), bCopy()
  11. 'FixStr100ArrCopy a1(), b1Copy()
  12.  
  13.  
  14. FOR i = 1 TO 20
  15.     PRINT i, bCopy(i) ', _TRIM$(b1Copy(i))
  17.  
  18. SUB sngArrCopy (A!(), copyB!())
  19.     REDIM copyB!(LBOUND(a!) TO UBOUND(a!)) 'container for _memget is ready
  20.     DIM m AS _MEM
  21.     m = _MEM(A!())
  22.     _MEMGET m, m.OFFSET, copyB!()
  24.  
  25. 'this wont work C++ doesn't like it
  26. 'SUB FixStr100ArrCopy (A() AS STRING * 100, copyB() AS STRING * 100)
  27. '    REDIM copyB(LBOUND(a) TO UBOUND(a)) AS STRING * 100 'container for _memget is ready
  28. '    DIM m AS _MEM
  29. '    m = _MEM(A())
  30. '    _MEMGET m, m.OFFSET, copyB()
  31. 'END SUB
  32.  
  33.  

Well at least I can copy a Single Array.
Title: Re: My First Attempt with MEM
Post by: Petr on September 06, 2019, 06:00:44 pm
Hi BPlus. I create it so:

Code: QB64: [Select]
  1. _TITLE "Mem test for array copy" 'B+ 2019-09-06
  2. DIM a(1 TO 20), a1(1 TO 20) AS STRING * 100 'cant do variable length strings , apparently not fixed strings either
  3. REDIM bCopy(0), b1Copy(0) AS STRING * 100
  4.  
  5. FOR i = 1 TO 20
  6.     a(i) = INT(10000 * RND) / 100
  7.     a1(i) = STR$(a(i))
  9.  
  10. sngArrCopy a(), bCopy()
  11. FixStr100ArrCopy a1(), b1Copy()
  12.  
  13.  
  14. FOR i = 1 TO 20
  15.     PRINT i; bCopy(i); _TRIM$(b1Copy(i))
  16.     SLEEP
  18.  
  19. SUB sngArrCopy (A!(), copyB!())
  20.     REDIM copyB!(LBOUND(a!) TO UBOUND(a!)) 'container for _memget is ready
  21.     DIM m AS _MEM
  22.     m = _MEM(A!())
  23.     _MEMGET m, m.OFFSET, copyB!()
  25.  
  26. 'this wont work C++ doesn't like it
  27. SUB FixStr100ArrCopy (A() AS STRING * 100, copyB() AS STRING * 100)
  28.     REDIM copyB(LBOUND(a) TO UBOUND(a)) AS STRING * 100 'container for _memget is ready
  29.     DIM n AS _MEM
  30.     n = _MEM(A())
  31.     DIM ch AS STRING
  32.     FOR i = 1 TO 20
  33.         ch$ = _MEMGET(n, n.OFFSET + (i - 1) * 99, STRING * 100)
  34.         copyB(i) = ch$
  35.     NEXT
  37.  
  38.  
  39.  
  40.  
Title: Re: My First Attempt with MEM
Post by: Petr on September 06, 2019, 06:04:18 pm
It works, but I still think the FOR NEXT loop is going to take speed down. I'm sure Steve will do it at least 80 times faster :)
Title: Re: My First Attempt with MEM
Post by: bplus on September 06, 2019, 06:51:19 pm
Hi Petr,

Yeah, I was hoping to get it all in one bite, like scooping up a Binary File.
Title: Re: My First Attempt with MEM
Post by: SMcNeill on September 06, 2019, 08:03:34 pm
Quote from: bplus on September 06, 2019, 05:26:39 pm
I tried to extend it to strings?, nope, fixed strings? nope, unless I am doing something wrong?

Variable length strings won't work with _MEM, as their position in memory is fluid and can move at any moment.  If you're directly accessing a pointer to a variable length string, you need to be aware that you're playing Russian Roulette with your program.  That memory can move between the time you get the _OFFSET for it, and the very next line when you try and use that _OFFSET to change/view it... 

Fixed length strings should work just fine with _MEM, and it seems you've probably discovered a bug in the command.  It'll need further testing and debugging, but unless Luke or Felippe knows some underlying reason I don't, we should be able to do what you were trying to do with your code. 

The way I'd normally do what you're trying to do is like so (and is probably why I've never encountered the glitch myself before):
Code: QB64: [Select]
  1. _TITLE "Mem test for array copy" 'B+ 2019-09-06
  2. DIM a(1 TO 20), a1(1 TO 20) AS STRING * 100 'cant do variable length strings , apparently not fixed strings either
  3. REDIM bCopy(0), b1Copy(0) AS STRING * 100
  4.  
  5. FOR i = 1 TO 20
  6.     a(i) = INT(10000 * RND) / 100
  7.     a1(i) = STR$(a(i))
  9.  
  10. sngArrCopy a(), bCopy()
  11. FixStr100ArrCopy a1(), b1Copy()
  12.  
  13.  
  14. FOR i = 1 TO 20
  15.     PRINT i, bCopy(i), _TRIM$(b1Copy(i))
  17.  
  18. SUB sngArrCopy (A!(), copyB!())
  19.     REDIM copyB!(LBOUND(a!) TO UBOUND(a!)) 'container for _memget is ready
  20.     DIM m AS _MEM
  21.     m = _MEM(A!())
  22.     _MEMGET m, m.OFFSET, copyB!()
  23.     _MEMFREE m
  25.  
  26. SUB FixStr100ArrCopy (A() AS STRING * 100, copyB() AS STRING * 100)
  27.     REDIM copyB(LBOUND(a) TO UBOUND(a)) AS STRING * 100 'container for _memget is ready
  28.     DIM m AS _MEM, m1 AS _MEM
  29.     m = _MEM(A()): m1 = _MEM(copyB())
  30.     _MEMCOPY m, m.OFFSET, m.SIZE TO m1, m1.OFFSET
  31.     _MEMFREE m
  32.     _MEMFREE m1

Just don't forget to _MEMFREE when you're finished, or else you're introducing a memory leak in your program which will accumulate and eventually lead to crashing after enough calls/repetitions. 
Title: Re: My First Attempt with MEM
Post by: bplus on September 06, 2019, 08:47:51 pm
Thanks Steve, I like breaking new ground.
Title: Re: My First Attempt with MEM
Post by: SMcNeill on September 06, 2019, 08:56:35 pm
Quote from: bplus on September 06, 2019, 08:47:51 pm
Thanks Steve, I like breaking new ground.

Just curious, but can’t  you also just do this, in this instance:

B() = A()
Title: Re: My First Attempt with MEM
Post by: bplus on September 06, 2019, 09:00:08 pm
Ha! for some reason I thought I couldn't I thought I tried a long long time ago with a Life variation...

hmm well this easy enough to check!

Nope!
Code: QB64: [Select]
  1. DIM a(1 TO 20), b(1 TO 20)
  2.  
  3. FOR i = 1 TO 20
  4.     a(i) = INT(10000 * RND) / 100
  6.  
  7. b() = a()
  8. FOR i = 1 TO 20
  9.     PRINT i, b(i)
  11.  

Neither with Dynamic arrays:
Code: QB64: [Select]
  1. REDIM a(1 TO 20), b(1 TO 20)
  2.  
  3. FOR i = 1 TO 20
  4.     a(i) = INT(10000 * RND) / 100
  6.  
  7. b() = a()
  8. FOR i = 1 TO 20
  9.     PRINT i, a(i), b(i)
  11.  
  12.  

It is curious that the first element does copy ??
Title: Re: My First Attempt with MEM
Post by: bplus on September 06, 2019, 09:14:51 pm
More notes from Steve's extended lesson (IRC) on _MEM stuff,

Along with _MEMCOPY, there is also _MEMFILL added to end of main:

Code: QB64: [Select]
  1. _TITLE "Mem test for array copy" 'B+ 2019-09-06
  2.  
  3. ' Don't forget _Memfree
  4.  
  5. DIM a(1 TO 20), a1(1 TO 20) AS STRING * 100 'cant do variable length strings , apparently not fixed strings either
  6. REDIM bCopy(0), b1Copy(0) AS STRING * 100
  7.  
  8. FOR i = 1 TO 20
  9.     a(i) = INT(10000 * RND) / 100
  10.     a1(i) = STR$(a(i))
  12.  
  13. sngArrCopy a(), bCopy()
  14. FixStr100ArrCopy a1(), b1Copy()
  15. FOR i = 1 TO 20
  16.     PRINT i, bCopy(i), _TRIM$(b1Copy(i))
  18.  
  19. 'example Steve's for MemFill
  20. DIM b(1 TO 10) AS INTEGER, m AS _MEM
  21. m = _MEM(b())
  22. _MEMFILL m, m.OFFSET, m.SIZE, &HFFFE AS INTEGER '<--- Presto!  It's now full with 10 values of 65535 (&HFFFF)
  23. FOR i = 1 TO 10
  24.     PRINT b(i)
  27.  
  28.  
  29. SUB sngArrCopy (A!(), copyB!())
  30.     REDIM copyB!(LBOUND(a!) TO UBOUND(a!)) 'container for _memget is ready
  31.     DIM m AS _MEM
  32.     m = _MEM(A!())
  33.     _MEMGET m, m.OFFSET, copyB!()
  34.     _MEMFREE m '<<<<<<<<<<<<<<<<<<<<<<<<<< like freeimage very important
  36.  
  37. 'this wont work C++ doesn't like it
  38. 'SUB FixStr100ArrCopy (A() AS STRING * 100, copyB() AS STRING * 100)
  39. '    REDIM copyB(LBOUND(a) TO UBOUND(a)) AS STRING * 100 'container for _memget is ready
  40. '    DIM m AS _MEM
  41. '    m = _MEM(A())
  42. '    _MEMGET m, m.OFFSET, copyB()
  43. 'END SUB
  44.  
  45. 'Steve's fix for strings
  46. SUB FixStr100ArrCopy (A() AS STRING * 100, copyB() AS STRING * 100)
  47.     REDIM copyB(LBOUND(a) TO UBOUND(a)) AS STRING * 100 'container for _memget is ready
  48.     DIM m AS _MEM, m1 AS _MEM
  49.     m = _MEM(A()): m1 = _MEM(copyB())
  50.     _MEMCOPY m, m.OFFSET, m.SIZE TO m1, m1.OFFSET
  51.     _MEMFREE m
  52.     _MEMFREE m1
  54.  
  55.  
  56.  
Title: Re: My First Attempt with MEM
Post by: Petr on September 07, 2019, 04:27:44 am
Also, thank you Steve for showing me how to do it better.
Title: Re: My First Attempt with MEM
Post by: Ashish on September 07, 2019, 10:00:49 am
Yeah! Thanks Steve for this. I had learned about _MEM from his (Steve) and Walter codes.
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