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Topic: Using PTR#A (Read 848 times) |
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GordonSweet
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Posts: 23
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Using PTR#A
« Thread started on: Nov 21st, 2008, 10:23am » |
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I can read all the bytes in say a TXT file like below or any other file. But how do I calculate the PTR#A to use BPUT#A to change a byte, or must I open the file for random access etc with fnum=OPENUP(filename$)
Thanks Gordon
Code:
MODE 20 : COLOUR 0,255,255,255 : CLS
COLOUR 7,0,0,0 : COLOUR 7
DIM dat(1000)
f$ = "1test.txt"
A=OPENIN f$
REPEAT
COLOUR 7 : c% = c% + 1 :
k% = BGET#A : dat(c%) = k%
IF k% > 31 AND k% <> 127 THEN PRINT CHR$(k%);
UNTIL EOF#A
CLOSE #A
END
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admin
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Posts: 1145
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Re: Using PTR#A
« Reply #1 on: Nov 21st, 2008, 1:27pm » |
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Quote:But how do I calculate the PTR#fnum to use BPUT#A to change a byte, or must I open the file for random access etc with fnum=OPENUP(filename$)
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You don't need to open a file with OPENUP to move its pointer; you can use PTR#fnum= to move the pointer whether the file was opened with OPENIN, OPENOUT or OPENUP. Obviously, when opened using OPENOUT you are restricted to moving the pointer to within the range you have already written.
As for calculating where to position the pointer, you should be able to work it out by knowing the number of bytes used for each item in the file. BPUT#fnum,n uses 1 byte, PRINT#fnum,n uses 5 bytes (in *FLOAT40 mode, 8 in *FLOAT64 mode) and PRINT#fnum,s$ uses LEN(s$)+1 bytes. Simply add together the sizes of the preceding items to find the current file pointer.
Richard.
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GordonSweet
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Re: Using PTR#A
« Reply #2 on: Nov 21st, 2008, 1:35pm » |
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Thanks again Richard I will study it.
Gordon
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GordonSweet
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Re: Using PTR#A
« Reply #3 on: Nov 22nd, 2008, 10:18am » |
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No luck Richard below shows Access Denied at line 210.
I expect I have got the length wrong Gordon
Code:
10 MODE 20 : COLOUR 0,255,255,255 : CLS
20 COLOUR 7,0,0,0 : COLOUR 7
30 DIM dat(10000) : f$ = "test.txt"
40
50 T=OPENOUT f$
60 PRINT#T, "Now is the time for all good men to come to the aid of the party."
70 CLOSE #T
80
90 dat = 5 : byte = 34 : length = 5
100 A=OPENIN f$
110 base=PTR#A
120 REPEAT
130 COLOUR 7 : c% = c% + 1
140 k% = BGET#A : dat(c%) = k%
150 IF k% > 31 AND k% <> 127 THEN PRINT " ";CHR$(k%);
160 UNTIL EOF#A OR c% > 30
170 @% = 3 : PRINT
180 FOR r = 1 TO 31 : PRINT r; : NEXT r : PRINT'
190 PTR# A=FN_ptr(dat)
200 BPUT#A,byte
210 CLOSE#A : RUN : REM To test
220 END
230
240 DEF FN_ptr(record)=base+record*length
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GordonSweet
Developer
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Re: Using PTR#A
« Reply #4 on: Nov 23rd, 2008, 07:31am » |
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Sorry to pester you Richard, I fathomed it out. The bytes here only increment by 1
Gordon
Code:
MODE 20 : COLOUR 0,255,255,255 : CLS
COLOUR 7,0,0,0 : COLOUR 7
f$ = "test.txt"
T=OPENOUT f$
PRINT#T, "Now is the time for all good men to come to the aid of the party."
CLOSE#T
PROCshow
REM insert
B=OPENUP f$
PTR#B=4 : BPUT#B,35
CLOSE#B
PROCshow
END
DEF PROCshow
A=OPENIN f$
INPUT#A,dat$ : PRINT dat$
CLOSE #A : ENDPROC
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