How to get GPS sentences to variable numbers

[TempodiBasic]

Hi acjacques
just to summarize all good tips coming from community...
here an idea to manage byte for byte the getting and the parsing of NMEA0183 sentence...

looking at here we can get more informations  https://en.wikipedia.org/wiki/NMEA_0183

Code: QB64: [Select]

1. ' Steve's suggestion
2. 'whole$ = "": byte$ = " "
3. 'DO
4. '   GET #1, , byte$
5. '   whole$ = whole$ + byte$
6. 'LOOP UNTIL byte$ = CHR$10)
7. 'whole$ = LEFT$(whole$, LEN(whole$) - 2)
8.  
9. 'But if we GET one byte$ at time we can just separate each element of the sentence now!
10.  
11. 'But since the NMEA sentences are a stream of characters with no fixed length how capture the whole sentence  ?
12.  
13. 'so
14. 'A tipical GPS sentence is like the following serial stream:
15. '$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A   (followed by CR +LF)
16. 'CONST CR = CHR$(13), LF = CHR$(10), Start = CHR$(36), CheckSum = CHR$(42), Comma = CHR$(44)
17. CONST CR = "
18. ", LF = "
19. ", Start = "$", CheckSum = "*", Comma = ","
20. DIM Byte AS STRING * 1, Sentence AS STRING, StringGPS(1 TO 100) AS STRING
21. DIM Index AS INTEGER
22. _CONTROLCHR OFF
23.  
24. IniT
25. OPEN "I.txt" FOR BINARY AS #1
26. SearchStartSentence
27. GettingFields
28. CLOSE #1
29. ShowResults
30. END
31.  
32.  
33.  
34. SUB IniT
35.     IF _FILEEXISTS("I.txt") THEN KILL "I.txt" 'EXIT SUB
36.     SHARED Sentence AS STRING, Byte AS STRING * 1
37.     Sentence = "$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A" + CR + LF
38.     OPEN "I.txt" FOR OUTPUT AS #1
39.     PRINT #1, Sentence
40.     CLOSE #1
41.     OPEN "I.txt" FOR INPUT AS #1
42.     LINE INPUT #1, Sentence
43.     PRINT Sentence
44.     CLOSE #1
45.     Byte = ""
46.     Sentence = ""
47.     PRINT "press a key to elaborate NMEA 0183 sentence..": SLEEP
48. END SUB
49.  
50. SUB ShowResults
51.     SHARED Index AS INTEGER, StringGPS() AS STRING, Sentence AS STRING
52.     DIM A AS INTEGER
53.     LOCATE 3, 1: COLOR 14, 1: PRINT Sentence
54.     COLOR 12, 1
55.     FOR A = 1 TO Index
56.         LOCATE , 10: PRINT StringGPS(A), "Index "; A
57.     NEXT
58. END SUB
59.  
60.  
61. SUB GettingFields
62.     SHARED Byte AS STRING * 1, Index AS INTEGER, StringGPS() AS STRING, Sentence AS STRING
63.     DIM A AS INTEGER
64.     WHILE Byte <> LF AND Byte <> CR
65.         Index = Index + 1
66.         WHILE Byte <> Comma AND Byte <> CheckSum AND Byte <> CR
67.             StringGPS(Index) = StringGPS(Index) + Byte
68.             Byte = TakeByte$
69.         WEND
70.         Byte = TakeByte$ ' read next character after delimitator "," or "*"  or CR
71.     WEND
72.     FOR A = 1 TO Index
73.         Sentence = Sentence + "\" + StringGPS(A)
74.     NEXT
75. END SUB
76.  
77. SUB SearchStartSentence
78.     SHARED Byte AS STRING * 1
79.     WHILE Byte <> Start
80.         Byte = TakeByte$
81.     WEND
82. END SUB
83.  
84. FUNCTION TakeByte$
85.     DIM Byte AS STRING * 1
86.     GET #1, , Byte
87.     TakeByte$ = Byte
88. END FUNCTION
89.  

this code example creates a txt file containing the example sentence posted by you here and terminated by CF+LF, if file doesn't exist and then go on to read byte for byte and translate the sentence in single fields until the checksum.
Naturally output is on the screen and the fields are in string so you can get value converting string to number using the right variable on the basis of the nature of the number got from sentence.

Thanks to read and try

PS Please don't rem CONST activated and don't unrem CONST deactivated... CHR$ is a internal function and QB64 doesn't like for now to use functions with CONST except some type of color functions if used in a choose manner