How to read a file in a timer function in Visual C++ using .NET

[bmerlover]

How can you read a file in a timer function? I am currently using a do while statement to read a file which works fine. The implementation is in C but I've added the code to a C++ .NET framework GUI app. This is the implementation that works:

void findPacketHeaders(char *inputFile, char *outputFile)
{
	/* Open file */
	fpInput = fopen(inputFile, "rb");
	fpOutput = fopen(outputFile, "w");
	
	/* check if fpInput exists */
	if (!fpInput)
	{
		fprintf(stderr, "Unable to open file %s", inputFile);
		return;
	}


	/* Read fpInput contents into buffer */
	do 
	{

		if (fgetc(fpInput) == 0x25 && fgetc(fpInput) == 0xEB)
		{

			getPacketHeaderSegments(fpInput, pktHeader, fpOutput);
		}
	
	}while(!feof(fpInput));


	fclose(fpInput);
	fclose(fpOutput);
}

What I would like to do is implement this in a timer function so that the computer won't lag because the file I open is very large and when its reading the file with the do while, the CPU usage goes to 100% with no response although it does finish after a while. I have used timer functions in the passed to solve "while" issues but I can't seem to get it to read this file.

FILE *fpInput, *fpOutput;
packetHeader pktHeader;

are global variables and they do work correctly.

This is my implementation of the timer:

void findPacketHeaders(char *inputFile, char *outputFile)
{
	//FILE *fpInput, *fpOutput;
	//packetHeader pktHeader;

	pktHeader.packetSyncPattern = 0xEB25;

	/* Open file */
	fpInput = fopen(inputFile, "rb");
	fpOutput = fopen(outputFile, "w");
	
	/* check if fpInput exists */
	if (!fpInput)
	{
		fprintf(stderr, "Unable to open file %s", inputFile);
		return;
	}

	processTimer->Interval = 10;
	processTimer->Enabled = true;

	fclose(fpInput);
	fclose(fpOutput);

}

private: System::Void processTimer_Tick(System::Object^  sender, System::EventArgs^  e) 
		 {
			/* Read fpInput contents into buffer */
			richTextBox_console->AppendText(fgetc(fpInput).ToString("X") + "\n");
			
			if (fgetc(fpInput) == 0x25 && fgetc(fpInput) == 0xEB)
			{

				getPacketHeaderSegments(fpInput, pktHeader, fpOutput);				
			}

			if(feof(fpInput))
			{
				/* break out of this */
				processTimer->Enabled = false;
			}

		 }

[\CODE]

[madankarmukta]

Hi..

Did you tried debugging this functions..?

That may help you a lot..!!

Thanks!

[bmerlover]

Well, I tried printing what fgetc outputs which is -1 all the time or the hex representation is FFFFFFFF. It seems like the fgetc isn't working correctly inside the timer function.

[tlhintoq]

Maybe you should read the file on a different thread and raise an event when it is done. Sure enough duct tape can fix anything, but patches on top of patches is never the way to go.

[bmerlover]

I found out what the problem was, when the timer started, the file was already closed because of the fclose statements at the bottom of findPacketHeade r. So I rearranged the code to something similar to this. Thanks for replying, I appreciate the inputs.

void findPacketHeaders(char *inputFile, char *outputFile) 
{ 
    pktHeader.packetSyncPattern = 0xEB25; 
  
    /* Open file */ 
    fpInput = fopen(inputFile, "rb"); 
    fpOutput = fopen(outputFile, "w"); 
  
    /* check if fpInput exists */ 
    if (!fpInput) 
    { 
        fprintf(stderr, "Unable to open file %s", inputFile); 
        return; 
    } 
  
    processTimer->Interval = 10; 
    processTimer->Enabled = true; 
 
} 
  
private: System::Void processTimer_Tick(System::Object^  sender, System::EventArgs^  e)  
         { 
            /* Read fpInput contents into buffer */ 

            if (fgetc(fpInput) == 0x25 && fgetc(fpInput) == 0xEB) 
            { 
  
                getPacketHeaderSegments(fpInput, pktHeader, fpOutput);                 
            } 
  
            if(feof(fpInput)) 
            { 
                /* break out of this */ 
                processTimer->Enabled = false; 

                fclose(fpInput); 
                fclose(fpOutput); 
  
            } 
  
         }