Windows 7 GetCommState keeps failing with error ERROR_INVALID_FUNCTION

[Dwigt]

I am using a Windows 7 machine, and I am trying to follow the C++ example posted here: http://msdn.microsoft.com/en-us/library/aa363201(v=VS.85).aspx and I keep entering this if statement
fSuccess = GetCommState(hCom, &dcb);

if (!fSuccess)
{
// Handle the error.
printf ("GetCommState failed with error %d.\n", GetLastError());
return (2);
}

And GetLastError returns 1, which I think means ERROR_INVALID_FUNCTION. What does that mean and how do I fix it?

 

[ChatGPT]

The error code ERROR_INVALID_FUNCTION (error code 1) typically means that a function was called with an invalid parameter. In the context of your code snippet, the issue could be related to how GetCommState() is being used or configured. Here are a few steps you can take to troubleshoot and potentially resolve this issue:

1. Check Parameters: Ensure that the parameters being passed to the GetCommState() function are correct and valid. The function expects a handle to a communications device (hCom) and a pointer to a DCB structure (&dcb).
2. Verify Handle: The handle hCom should be a valid handle to the communications device. Make sure that it is properly initialized and opened before calling GetCommState().
3. DCB Structure: The DCB structure (dcb) should be properly initialized before passing it to GetCommState(). Ensure that you have properly set the size of the DCB structure using dcb.DCBlength = sizeof(DCB).
4. Permissions: Ensure that the application has the necessary permissions to access the communications device. This may require administrative privileges depending on the device and its configuration.
5. Error Handling: Improve error handling in your code to provide more specific information about failures. You can add additional checks and error messages to pinpoint where the issue occurs.
6. Update Device Drivers: Ensure that the drivers for the communications device are up-to-date. Outdated or incompatible drivers can sometimes cause such errors.
7. Compatibility: Since you are using Windows 7, ensure that the code you are trying to run is compatible with this operating system. Compatibility issues can arise if the code is designed for a different version of Windows. By following these steps and checking the parameters, handle, structure initialization, permissions, and drivers, you can potentially diagnose and fix the ERROR_INVALID_FUNCTION issue you are facing. If the issue persists, further debugging and detailed analysis may be required to identify the root cause.