Exception order

[Airslash]

Hello,

I have an issue with the order of Exceptions. Currently my application just dies instead of handeling the one Exception it was supposed to catch, so I added additional try-catch statements to handle the errors.

Here is the outer part of the code

		// We have to supply a new image ID because on every drive we
		// rewrite from 0.
		try
		{
			try
			{
				Path = DriveToUse->WriteImage(&TmpId, FileFormat, Buffer);
			}
			catch(std::exception &ex)
			{
				// Log the error message.
				ShowMessage("Exception got caught");
//				Logger::getSingletonPtr()->writeMsg(Ex.Message, 0, LOG_ERROR, true);
//				Logger::getSingletonPtr()->writeLogMsg(Ex.Message, 0, LOG_ERROR, true, TDateTime::CurrentDate());

				// Update the RecordId to skip over the following disk.
				// If this is the last disk, then the recordID needs to
				// be set to 0, else to the JumpPoint of the disk.
				if(mDrives.back() == DriveToUse)
				{
					RingBuffer::Instance()->changeRecNr(0);
				}
				else
				{
					long NewId = CalculatePreviousJumpPoint(DriveToUse) + DriveToUse->MaximumImages();
					RingBuffer::Instance()->changeRecNr(NewId);
				}

				// Call ourselves again, and try a new disk.
				Path = WriteAnalogueImage(FileFormat, Buffer);
			}

			// Return true.
			return Path;
			}
		catch(...)
		{
            ShowMessage("AMAGAD SOMETHING UNKNOWN HAPPENDED!");
        }
	}

This function calls the WriteImage method on my Drive object. That function uses a library to access the hardware we use for talking to Cameras.
This is the code of that function

AnsiString IO::Drive::WriteImage(long* RecordId, long FileFormat, MIL_ID Buffer)
{
	// Call the MIL function to write the file.
	// Save the complete path and return it later on.
	AnsiString Path = AnsiString(DriveLetter()) + ":\\Images\\";
	AnsiString Folder = AnsiString(IntToHex((int)(*RecordId / 0xFFF), 3)) + "\\";
	AnsiString Filename = AnsiString(IntToHex((int)(*RecordId % 0xFFF), 3)) + ".jpg";

	// Check if this directory exits, create it if it doesnt.
	if(!DirectoryExists(Path + Folder))
	{
		ForceDirectories(Path + Folder);
	}

	// Export the buffer to the image.
	// Try to save the data from the buffer to a file on the disk.
	MbufExport((Path + Folder + Filename).c_str(), FileFormat, Buffer);

	// Get the last error returned from the MIL system, this way we can check
	// if the previous function executed properly.
	long MilErrorCode = MappGetError(M_CURRENT, M_NULL);

	// Check if an error occured. If the value is M_NULL_ERROR then no
	// error occured with the last function call.
	if(M_NULL_ERROR == MilErrorCode)
	{
		return (Path + Folder + Filename);
	}
	else
	{
		ShowMessage("ErrorCode returned = " + AnsiString(MilErrorCode) + " :: M_NULL_ERROR = " + AnsiString(M_NULL_ERROR));
		// Writing failed. throw a new excption
		// and mark ourselves as unusable.
		SetUsable(false);

		// Throw the exception so we can catch it in the manager.
		throw new Exception("Failed to write the file to the disk. ErrorCode : " + AnsiString(MilErrorCode));
	}
}

When I ran the code and pulled out a harddrive this is the errormessages I got, in sequence:

- AMAGAD SOMETHING UNKNOWN HAPPENED
- ErrorCode Returned = 58, M+NULL_ERROR = 0
- Caught an Exception

I don't understand why they come in this order....
I expected the following order of messages:

- ShowMessage()
- Caught an Exception
- AMAGAD.

[Banfa]

Don't new the exception, not this

throw new Exception("Fail ed to write the file to the disk. ErrorCode : " + AnsiString(MilE rrorCode));

but this

throw Exception("Fail ed to write the file to the disk. ErrorCode : " + AnsiString(MilE rrorCode));

Because the compiler can not match Exception& and Exception* as the same type. You should be catching by reference (See More Effective C++ by Scott Meyers for the reasons) so you have to throw an object not a pointer.

[Airslash]

aah cool,

wil definitly remember that for my next version.
At the moment I removed the exceptions and used pointer to fill the variables and have my functions return a bool to signal success or failure