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JerryR
Joined: 07 Feb 2008
Posts: 164
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| A little guidance using strtok please |
 Posted: Thu Mar 27, 2008 10:23 am |
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I am attempting to parse comma separated fields from a GPS-generated (nmea-0183) array of chars using strtok. I am running into a problem that I need help with. Using 3.249 PCWH compiling code for a PIC18F4525 controller.
Here a code snippet:
| Code: |
{
float UTC; //Complete UTC float
int8 UTC_Hours; //UTC hours
int8 UTC_Mins; //UTC min
int8 UTC_Secs_Int; //UTC seconds
int16 UTC_Secs_Frac; //UTC frac seconds
char Status;
float Lat; //Complete Lat. float
int8 Lat_Deg; //Lat. Degrees
int8 Lat_Min; //Lat. Minutes
int16 Lat_Min_Frac; //Lat. Frac Minutes
char N_S; //North =1, S =0
float Lon; //Complete Lon. float
int8 Lon_Deg; //Long. Degrees
int8 Lon_Min; //Long. Minutes
int16 Lon_Min_Frac; //Long. Frac Minutes
char E_W; //East =1, W =1
float Speed; //Complete speed float
float Course; //Complete course float
int32 Date; //complete date
int8 Rx_CheckSum; //8 bit checksum received
char Term[1];
int8 Index;
char *Field;
strcpy(Term,","); //load delimiter ","
Field = strtok(Working_GPS_Str, Term); //parse to next delimiter
UTC = atof(strtok(0, Term)); //get UTC time float
Status = strtok(0, Term); //get status char (A or V)
Lat = atof(strtok(0, Term)); //get latitude float
N_S = strtok(0, Term); //get N_S char (N or S)
Lon = atof(strtok(0, Term)); //get longitude float
E_W = strtok(0, Term); //get E_W char (E or W)
Speed = atof(strtok(0, Term)); //get speed float
Course = atof(strtok(0, Term)); //get course float
Date = atoi32(strtok(0, Term)); //get date
delay_us(1); //stopping point for
//debugger
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The ASCII string to parse is:
$GPRMC,161229.487.A,3723.2475,N,12158.3416,W,0.13,309.62,120598,,*10
All number (float) are parsed fine. However the "A", "N", "W" are parsed incorrectly. The results are: Status= '2' (0x32), N_S= '>', and E_W= 'K'.
Anyone see my mistake?
Thanks in advance! |
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Matro
Guest
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| Posted: Thu Mar 27, 2008 10:34 am |
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Just add a line at the beginning where you set the string to parse. Just to see if the problem isn't there. Use a constant string for demo.
Matro. |
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JerryR
Joined: 07 Feb 2008
Posts: 164
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| Posted: Thu Mar 27, 2008 10:57 am |
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Thanks for the quick reply Matro. Good suggestion, but still same result. The solution will probably be pretty simple. Here's the code with the "canned" GPS string forced into it.
| Code: |
Parse_CkSum_GPS(*Working_GPS_Str)
{
float UTC; //Complete UTC float
int8 UTC_Hours; //UTC hours
int8 UTC_Mins; //UTC min
int8 UTC_Secs_Int; //UTC seconds
int16 UTC_Secs_Frac; //UTC frac seconds
char Status;
float Lat; //Complete Lat. float
int8 Lat_Deg; //Lat. Degrees
int8 Lat_Min; //Lat. Minutes
int16 Lat_Min_Frac; //Lat. Frac Minutes
char N_S; //North =1, S =0
float Lon; //Complete Lon. float
int8 Lon_Deg; //Long. Degrees
int8 Lon_Min; //Long. Minutes
int16 Lon_Min_Frac; //Long. Frac Minutes
char E_W; //East =1, W =1
float Speed; //Complete speed float
float Course; //Complete course float
int32 Date; //complete date
int8 Rx_CheckSum; //8 bit checksum received
char Term[1];
int8 Index;
char *Field;
strcpy (Working_GPS_Str, "GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0.13,309.62,120598");
strcpy(Term,","); //load delimiter ","
Field = strtok(Working_GPS_Str, Term); //parse to next delimiter
UTC = atof(strtok(0, Term)); //get UTC time float
Status = strtok(0, Term); //get status char (A or V)
Lat = atof(strtok(0, Term)); //get latitude float
N_S = strtok(0, Term); //get N_S char (N or S)
Lon = atof(strtok(0, Term)); //get longitude float
E_W = strtok(0, Term); //get E_W char (E or W)
Speed = atof(strtok(0, Term)); //get speed float
Course = atof(strtok(0, Term)); //get course float
Date = atoi32(strtok(0, Term)); //get date
delay_us(1);
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JerryR
Joined: 07 Feb 2008
Posts: 164
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| Posted: Thu Mar 27, 2008 11:02 am |
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And another thing... It doesn't matter what character I put in the "A" position, the result for Status is still '2' (ASCII).
Any other thoughts? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Mar 27, 2008 11:07 am |
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Strip the program down to essentials. Use a very short test string
that consists just of "A,B,C" or something like that. Get rid of most
of those variables. Then try to parse out the A,B,C chars. Post a
complete, compilable test program, with the #include,#fuses, #use
delay, and a main() and the printf() statement that displays the result
of the parsing. In other words, post a (very short -- 10 lines) program
that I can copy and paste into MPLAB and run in the MPSIM simulator.
Also post your compiler version. |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Thu Mar 27, 2008 11:29 am |
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| Code: | char Term[1];
...
strcpy(Term,","); //load delimiter "," |
Your Term array should be large enough to contain the string + terminating zero. Now it is 1 character too small and strcpy will overwrite memory with unpredictable results.
Second problem: | Code: | | Status = strtok(0, Term); //get status char (A or V) |
Strtok returns a pointer, not a value. |
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JerryR
Joined: 07 Feb 2008
Posts: 164
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| Posted: Thu Mar 27, 2008 12:08 pm |
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ckielstra, PCM:
Thanks for your replies. Yes, Yes strtok returns a pointer! I dropped my "*".
Thanks so much! |
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Matro
Guest
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| Posted: Thu Mar 27, 2008 12:14 pm |
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I just think the same thing.
strtok() returns a pointer and not a value.
That's why it works when you use atof() that takes a pointer too in parameter.
Use that code:
| Code: |
UTC = atof(strtok(0, Term)); //get UTC time float
Status = *strtok(0, Term); //get status char (A or V)
Lat = atof(strtok(0, Term)); //get latitude float
N_S = *strtok(0, Term); //get N_S char (N or S)
Lon = atof(strtok(0, Term)); //get longitude float
E_W = *strtok(0, Term); //get E_W char (E or W)
Speed = atof(strtok(0, Term)); //get speed float
Course = atof(strtok(0, Term)); //get course float
Date = atoi32(strtok(0, Term));
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Matro |
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Guest
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| Thanks Matro |
| Posted: Thu Mar 27, 2008 12:33 pm |
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Matro:
Yes, that's what I did to fix it. I didn't catch the pointer issue!
Thanks for your interest! |
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