Error writing to file (fopen) in WinCE7 - c

Question

I am developing an application in WinCE7. The application includes a serial com port and file IO operations. There is an embedded device connected the serial port. I need to check the status of inputs on the device and save their details in file. Lets say, if input 1 is high then I need to write Input 1 HIGH on the serial port, and save the same in file.
Now to write data in file I am using fprintf & fopen functions. Code looks like below:
main()
{
// some code to initialize serial port
FILE * fp;
fp= fopen ("Logs.txt", "w+"); //-------> create a file named as Logs.txt
while(1)
{
if(Input1 == TRUE)
{
serialPort.Send("Input 1 HIGH");
fprintf(fp,"%s","Input 1 HIGH"); //-------> saving data in file
}
if(Input2 == TRUE)
{
serialPort.Send("Input 2 HIGH");
fprintf(fp,"%s","Input 2 HIGH"); //-------> saving data in file
}
//same goes for rest of the inputs
}
fclose(fp); //----------> closing the file
}
Now after writing data to the file using fprintf, we need to use fclose() to close the file. But as I have to continuously monitor the input status I have used while(1) due to which my control doesn't reaches at fclose(fp). Thus the file is not closed and it becomes corrupted. When I open the file to see the saved data it gave me below error:
How can I properly use flcose() and fprintf() to write data in file.?

Answer 1

There is nothing wrong with opening log file and closing each time you want to do the logging. It might cause problems if your while loop is being executed with very high frequency - it may slow down your application. This is why you should consider a way to somehow close your application, now as I understand you copy your log file while your application is being executed - this can cause all sort of problems - among others that your file will be corrupted.
btw. you can also use windows-ce native logging api like: CeLog, see here:
https://msdn.microsoft.com/en-us/library/ee479601.aspx
https://msdn.microsoft.com/en-us/library/ee488587.aspx

Answer 2

When would your loop start, and when would it end? I mean, not programatically, but theoretically? The simplest thing seems to be to modify the while condition. As of now, it will be endlessly stuck in the while loop!
Lets assume that your program is running, and it keeps on running for as long as your device remains connected. So you need to monitor some message or look for some event that signifies that the device has disconnected or stopped (or whatever is appropriate). This event or situation can be used as a flag (for eg., TRUE while the device is connected and active, FALSE when the device is disconnected or inactive) and then use that as a condition to open/write/close the file.
Further more, instead of a loop, you could use a timer or a periodic event to poll your device input. You can adjust your polling rate as high as you like, depending on the accuracy of your timer. This will ensure that your code doesn't get stuck in a loop. Say, you call your function to monitor the input at every timer tick. So each time the tick event fires, the input will be read. And you can check the condition of the device's connection before calling the polling function.
the flow would go something like:
Start->Device connected, flag TRUE->fOpen->Start timer
=>timer tick->flag == TRUE?->poll device->write to file=> (repeats for each tick unless the below scenario happens.)
Device disconnected, flag FALSE
=>timer tick->flag == TRUE? NO->fClose->Stop timer->Stop
This would assume that you had some way of detecting the device connect/active vs disconnect/inactive situations. Maybe the device SDK has some form of message or event that signifies this.