My First Attempt with MEM

[bplus]

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$(a(i))
8. NEXT
9.  
10. sngArrCopy a(), bCopy()
11. 'FixStr100ArrCopy a1(), b1Copy()
12.  
13.  
14. FOR i = 1 TO 20
15.     PRINT i, bCopy(i) ', _TRIM$(b1Copy(i))
16. NEXT
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. END SUB
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.

[Petr]

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$(a(i))
8. NEXT
9.  
10. sngArrCopy a(), bCopy()
11. FixStr100ArrCopy a1(), b1Copy()
12.  
13.  
14. FOR i = 1 TO 20
15.     PRINT i; bCopy(i); _TRIM$(b1Copy(i))
16.     SLEEP
17. NEXT
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!()
24. END SUB
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
36. END SUB
37.  
38.  
39.  
40.  

[Petr]

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 :)

[bplus]

Hi Petr,

Yeah, I was hoping to get it all in one bite, like scooping up a Binary File.

[SMcNeill]

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$(a(i))
8. NEXT
9.  
10. sngArrCopy a(), bCopy()
11. FixStr100ArrCopy a1(), b1Copy()
12.  
13.  
14. FOR i = 1 TO 20
15.     PRINT i, bCopy(i), _TRIM$(b1Copy(i))
16. NEXT
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
24. END SUB
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
33. END SUB

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. 

[bplus]

Thanks Steve, I like breaking new ground.

[SMcNeill]

Thanks Steve, I like breaking new ground.

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

B() = A()

[bplus]

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
5. NEXT
6.  
7. b() = a()
8. FOR i = 1 TO 20
9.     PRINT i, b(i)
10. NEXT
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
5. NEXT
6.  
7. b() = a()
8. FOR i = 1 TO 20
9.     PRINT i, a(i), b(i)
10. NEXT
11.  
12.  

It is curious that the first element does copy ??

[bplus]

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$(a(i))
11. NEXT
12.  
13. sngArrCopy a(), bCopy()
14. FixStr100ArrCopy a1(), b1Copy()
15. FOR i = 1 TO 20
16.     PRINT i, bCopy(i), _TRIM$(b1Copy(i))
17. NEXT
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)
25. NEXT
26. _MEMFREE m
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
35. END SUB
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
53. END SUB
54.  
55.  
56.  

[Petr]

Also, thank you Steve for showing me how to do it better.

[Ashish]

Yeah! Thanks Steve for this. I had learned about _MEM from his (Steve) and Walter codes.