CODEWITHSUNDEEP
c++
kevin
kevin

Reputation: 11

trouble decoding the serial GPS using readfile function

i m trying to use readfile function to read the serial port in c++. i manage to open and read the serial port in c++. the problem i facing now is the decoding of data after i read from the serial port. The below are my codes. When i run my code, my loop of decoding could not detect ((*&szChar == '$')), and it exit the loop by printing error. May i know how could i decode the gps data that i read from my serial port? thanks

char szChar[100];
int nRet;
DWORD  dwBytesRead = 10;
char   ReadBuffer[BUFFERSIZE] = {0};
nRet = ReadFile(hCom,&szChar,BUFFERSIZE-1,&dwBytesRead,NULL);
if((*&szChar == '$'))
{
    printf("%s\n", &szChar);
}
else
{
    printf("error\n");

Upvotes: 1

Views: 706

Answers (2)

kevin
kevin

Reputation: 11

@Jerry: Thanks.. so i edited my code below to decode my data, is it correct way to put my ReadBuffer into another array for checking? 

char lastCommaPosition;
char  latitudeString[11];
char     stringRead[MAXSIZE]; 
char  tempString[MAXSIZE];
char  *pChar;
char  dummyChar;
float        latitude;
int          latDegrees;
float        latMinutes;
int     numLinesRead;

int Ret,i,j,k; 
  if (ReadBuffer[0] == '$') 
{
    i = 0;
    numLinesRead++;
    stringRead[i] = ReadBuffer;

}
stringRead[i+1] = '\0';



j = 0;
pChar = stringRead;
while(*(pChar+j) != ',') 
{
       tempString[j] = *(pChar+j);
       j++;
 }
 tempString[j] = '\0';


if(tempString[3] == 'G' && tempString[4] == 'G' && tempString[5] == 'A')
{
     pChar = stringRead;


      j = lastCommaPosition + 1;
      k = 0;
      while(*(pChar+j) != ',') 
      {
       latitudeString[k] = *(pChar+j);
       j++;
       k++;
      }
      lastCommaPosition = j;
      latitudeString[k] = '\0';

      sscanf(latitudeString, "%f", &latitude);
      latDegrees = (int)(latitude/100);
      latMinutes = (float)(latitude - latDegrees*100);
      printf("\t%02d DEG\t%2.4f MIN", latDegrees, latMinutes);

Upvotes: 0

Jerry Coffin
Jerry Coffin

Reputation: 490663

I have to say, I find your code quite confused and confusing. Just for example, you're creating szChar as an array of 100 char, and ReadBuffer as an array of BUFFERSIZE chars. When you call ReadFile, however, you're passing the base address of szChar with the size given as BUFFERSIZE. Unless, by some coincidence, BUFFERSIZE happens to equal 100, that looks a lot like a potential buffer overrun.

Then we get to *&szChar. This doesn't really make much sense either. From the looks of things, you probably want szChar[0] -- but even that's not really a good idea, because you might not receive the data in exactly line-sized pieces. As such, you probably want to scan through the data to find the '$'.

int Ret;
DWORD  BytesRead;
char   ReadBuffer[BUFFERSIZE] = {0};
Ret = ReadFile(hCom,ReadBuffer,sizeof(ReadBuffer)-1,&BytesRead,NULL);

ReadBuffer[BytesRead] = '\0';

if (ReadBuffer[0] == '$')
    printf(%s\n", ReadBuffer);
else
    printf("error\n");

Upvotes: 1

Related Questions