Reading from serial port in C, having problems with ReadFile maybe? - c

Question

Well I've been at this program for maybe four hours. I've been trying to create a little program to read what my arduino Uno is spitting out through the serial port.
What I find odd is that the program works only AFTER I've launched the arduino IDE's built in serial monitor. Perhaps this is an issue with initializing the port correctly?
If someone could help me out it'd be much appreciated. The program seems to hang during ReadFile, so maybe there's an issue with permissions...
#include Windows.h>
#include stdio.h>
#include tchar.h>//Removed to allow for stackoverflow format
void printCommState(DCB d);
int main() {
DCB dcb = { 0 };
HANDLE hPort;
BOOL success;
TCHAR *commPort = TEXT("COM3");
char buffer[40] = { 0 };
DWORD dwBytesRead = 0;
DWORD dwBytesWrite = 0;
int l;
/*COMMTIMEOUTS cTimeOut;
cTimeOut.ReadIntervalTimeout = 50;
cTimeOut.ReadTotalTimeoutConstant = 50;
cTimeOut.ReadTotalTimeoutMultiplier = 10;
cTimeOut.WriteTotalTimeoutConstant = 50;
cTimeOut.WriteTotalTimeoutMultiplier = 10;*/
dcb.DCBlength = sizeof(DCB);
dcb.BaudRate = CBR_9600;//Found on microsofts website
dcb.ByteSize = DATABITS_8;// standardized number?
dcb.Parity = NOPARITY;// found in comp management
dcb.StopBits = 1;
/*dcb.fBinary = 1;
dcb.fDtrControl = 1;
dcb.fTXContinueOnXoff = 1;
dcb.fRtsControl = 1;
dcb.XonLim = 2048;
dcb.XoffLim = 512;
dcb.XoffChar = 2;*/
//dcb.fDtrControl = DTR_CONTROL_DISABLE;//maybe unnecessary?
printCommState(dcb);
hPort = CreateFile(commPort, // This comm port is defined by TCHAR so that we can use TEXT() LPFILENAME
GENERIC_READ | GENERIC_WRITE,//DesiredAccess
0,//dwShareMode
NULL,//LPSecurity
CREATE_NEW| OPEN_EXISTING,//dwCreationDisposition
0,//Flags and attributes
NULL);//hTemplateFile
if (hPort == INVALID_HANDLE_VALUE) {
printf("CreateFile failed with the error %d.\n", GetLastError());
scanf_s("%d", &l);
return 1;
}
success = GetCommState(hPort, &dcb);
if (!success) {
printf("GetCommState failed with the error %d.\n ", GetLastError());
scanf_s("%d", &l);
return 2;
}
success = SetCommState(hPort, &dcb);
if (!success) {
printf("SetCommState failed with error %d.\n", GetLastError());
scanf_s("%d", &l);
return 3;
}
/*TIME TO READ STUFF*/
while (GetCommState(hPort, &dcb)) {
printf("We're in the while statement\n");
//+=+=+=+=+=+POSSIBLE PROBLEM?
if (ReadFile(hPort, buffer, 39, &dwBytesRead, NULL)) {
//hFile,lpBuffer,NumberofBytesToRead,LPnumberofbytestoread,lpOverlapped
printf("We're in the ifReadFile Statement!\n");
for (int j = 0; j < sizeof(buffer); j++) {
printf("in the for loop!\n");
printf("%c", buffer[j]);
}
printf("\n");
}
if (!ReadFile(hPort, &buffer, 39, &dwBytesRead, NULL)) {
printf("Error with ReadFile %d\n.", GetLastError());
}
}
scanf_s("%d", &l);
CloseHandle(hPort);
return 0;
}
void printCommState(DCB d) {
printf("\nBaudRate: %d\tByteSize: %d\tParity: %d\tStopBits: %d\n",
d.BaudRate,
d.ByteSize,
d.Parity,
d.StopBits);
}

Answer 1

The issue lies in the GetCommState line of the code
GetCommState code function
Here we have it setting the DCB to the settings returned by that function, so by adding another DCB (dcbRecieving, for instance as an example ) just as an error-catching device and having GetCommState point to that other DCB, we can keep our error catching DCB and set our original to the other one, or set the new parameters after the if statement.
Anyways, thanks a ton!