trouble decoding the serial GPS using readfile function - c++

Question

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");

Answer 1

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");

Answer 2

#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);